.-bridge 
!.j  iological    Serie 


THE  VERTEBRATE  SKELETON 


MEDICAL    SCHOOL 


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WS*L 


M     4 


CAMBRIDGE    BIOLOGICAL    SERIES. 

GENERAL  EDITOR  : — ARTHUR  E.  SHIPLEY,  M.A. 

FELLOW   AND    TUTOR   OF    CHRIST'S    COLLEGE,    CAMBRIDGE. 


THE 

VERTEBRATE   SKELETON. 


EonUon:   C.  J.  CLAY  AXD  SONS, 

CAMBRIDGE   UNIVERSITY  PRESS   WAREHOUSE, 

AVE   MARIA  LANE, 

AND 

H.   K.   LEWIS, 
136,   GOWER   STREET,    W.C. 


ffilaggoto:   50,  WELLINGTON  STREET. 

JLtiyw:    F.  A.  BROCKHAUS. 
gork:    THE   MACMILLAN  COMPANY. 
anU  Calcutta:    MACMILLAN  AND  CO.,  LTD. 


[All  Rights  reserved.] 


THE 

VERTEBRATE   SKELETON 


BY 


SIDNEY   H.   REYNOLDS,   M.A., 

TRINITY    COLLEGE,    CAMBRIDGE  J 

LECTURER   AND    DEMONSTRATOR    IN    GEOLOGY   AND    ZOOLOGY   AT    UNIVERSITY 
COLLEGE,    BRISTOL. 


(Eambtfoge : 

AT   THE    UNIVERSITY    PRESS. 

1807 
J> 

[All  Rights  reserved.]  ' 


Cambridge : 


PRINTED   BY   J.    &    C.    F.    CLAY, 
AT    THE    UNIVERSITY    PRESS. 


QLS21 

-R46 

1397 


PEBFACE. 


IN  the  following  pages  the  term  skeleton  is  used  in  its 
widest  sense,  so  as  to  include  exoskeletal  or  tegumentary 
structures,  as  well  as  endoskeletal  structures.  It  was  thought 
advisable  to  include  some  account  of  the  skeleton  of  the 
lowest  Chordata — animals  which  are  not  strictly  vertebrates, 
but  it  seemed  undesirable  to  alter  the  title  of  the  book  in 
consequence. 

The  plan  adopted  in  the  treatment  of  each  group  has 
been  to  give  first  an  account  of  the  general  skeletal  characters 
of  the  group  in  question  and  of  its  several  subdivisions ; 
secondly  to  describe  in  detail  the  skeleton  of  one  or  more 
selected  types ;  and  thirdly  to  treat  the  skeleton  as  developed 
in  the  group  organ  by  organ. 

A  beginner  is  advised  to  commence,  not  with  the  intro- 
ductory chapter,  but  with  the  skeleton  of  the  Dogfish,  then 
to  pass  to  the  skeletons  of  the  Newt  and  Frog,  and  then 
to  that  of  the  Dog.  After  that  he  might  pass  to  the  intro- 
ductory chapter  and  work  straight  through  the  book.  I  have 
endeavoured  to  make  the  account  of  each  type  skeleton 
complete  in  itself;  this  has  necessitated  a  certain  amount  of 


6111 


VI  PREFACE. 

repetition, — a  fault  that  I  have  found  it  equally  difficult  to 
avoid  in  other  parts  of  the  book. 

Throughout  the  book  generic  names  are  printed  in  italics ; 
and  italics  are  used  in  the  accounts  of  the  type  skeletons  for 
the  names  of  membrane  bones.  Clarendon  type  is  used  to 
emphasise  certain  words.  In  the  classificatory  table  the 
names  of  extinct  genera  only,  are  printed  in  italics. 

In  a  book  in  which  an  attempt  is  made  to  cover  to  some 
extent  such  a  vast  field,  it  would  be  vain  to  hope  to  have 
avoided  many  errors  both  of  omission  and  commission,  and 
I  owe  it  to  the  kindness  of  several  friends  that  the  errors  are 
not  much  more  numerous.  I  cannot  however  too  emphatically 
say  that  for  those  which  remain  I  alone  am  responsible. 
Messrs  C.  W.  Andrews,  E.  Fawcett,  S.  F.  Harmer,  J.  Graham 
Kerr,  and  B.  Rogers  have  all  been  kind  enough  to  help  me 
by  reading  proofs  or  manuscript,  while  the  assistance  that  I 
have  received  from  Dr  Gadow  during  the  earlier  stages  and 
from  Prof.  Lloyd  Morgan  and  Mr  Shipley  throughout  the 
whole  progress  of  the  work  has  been  very  great.  To  all  these 
gentlemen  my  best  thanks  are  tendered. 

All  the  figures  except  1,  35,  55,  and  84  were  drawn  by 
Mr  Edwin  Wilson,  to  whose  care  and  skill  I  am  much  in- 
debted. The  majority  are  from  photographs  taken  by  my 
sister  Miss  K.  M.  Reynolds  or  by  myself  in  the  British 
Museum  and  in  the  Cambridge  University  Museum  of 
Zoology,  and  I  take  this  opportunity  of  thanking  Sir  W.  H. 
Flower  and  Mr  S.  F.  Harmer  for  the  facilities  they  have 
afforded  and  for  permission  to  figure  many  objects  in  the 
museums  respectively  under  their  charge.  I  have  also  to 
thank  (1)  Prof,  von  Zittel  for  permission  to  reproduce  figs.  27, 
41,  52,  69,  70,  80,  106  A,  and  107  c;  (2)  Sir  W.  H.  Flower 
and  Messrs  A.  and  C.  Black  for  figs.  1  and  84;  (3)  Prof.  O.  C. 


PREFACE.  vn 

Marsh  and  Dr  H.  Woodward  for  fig.  35 ;  (4)  Dr  C.  H.  Hurst 
and  Messrs  Smith,  Elder,  and  Co.  for  fig.  55. 

A  few  references  are  given,  but  no  attempt  has  been  made 
to  give  anything  like  a  complete  list.  The  abbreviations 
of  the  titles  of  periodicals  are  those  used  in  the  Zoological 
Record. 

I  have  always  referred  freely  to  the  textbooks  treating  of 
the  subjects  dealt  with,  and  in  particular  I  should  like  to 
mention  that  the  section  devoted  to  the  skeleton  of  mammals 
is,  as  it  could  hardly  fail  to  be,  to  a  considerable  extent  based 
on  Sir  W.  H.  Flower's  Osteology  of  the  Mammalia. 

SIDNEY  H.   REYNOLDS. 

March  10,  1897. 


CONTENTS. 


CHAPTER   I. 

PAGK 

Introductory  account  of  the  skeleton  in  general    ....         1 

CHAPTER   II. 

Classification 30 

CHAPTER   III. 

Skeleton  of  Hemichordata,  Urochordata  and  Cephalochordata      .       50 

CHAPTER   IV. 

Skeletal  characters  of  the  Vertebrata.     The  skeleton  in  the  Cyclo- 

stomata 53 

CHAPTER   V. 

Skeletal  characters  of  the  Ichthyopsida.     Characters  of  the  several 

groups  of  Pisces 59 

CHAPTER   VI. 

The  skeleton  of  the  Dogfish  (Scyllium  canicula)    ....       71 


X  CONTENTS. 

CHAPTER  VII. 

PAGE 

The  skeleton   of  the   Codfish  (Gadus   morrhua)  and   the   skull  of 

the  Salmon  (Salmo  salar]          .  83 

CHAPTER   VIII. 

General  account  of  the  skeleton  in  Fishes 104 

CHAPTER    IX. 

Characters  of  the  several  groups  of  Amphibia       ....     183 

CHAPTER    X. 

The  skeleton  of  the  Newt  (Molge  cristata) 138 

CHAPTER   XI. 

The  skeleton  of  the  Frog  (Eana  temporaria)  ....     151 

CHAPTER   XII. 

General  account  of  the  skeleton  in  Amphibia        .         .         .         .168 

CHAPTER   XIII. 

Skeletal  characters  of  the  Sauropsida.     Characters  of  the  several 

groups  of  Keptiles 189 

CHAPTER   XIV. 

The  skeleton  of  the  Green  Turtle  (Chelone  midas)         .         .         .     214 

CHAPTER   XV. 

The  skeleton  of  the  Crocodile  (Crocodilus  palustris)      .         .         .     237 

CHAPTER   XVI. 

General  account  of  the  skeleton  in  Keptiles 270 


CONTENTS.  XI 

CHAPTER   XVII. 

PAGE 

Characters  of  the  several  groups  of  Birds      .....     295 

CHAPTER   XVIII. 

The  skeleton  of  the  Wild  Duck  (Anas  boschas)      ....     302 

CHAPTER   XIX. 

General  account  of  the  skeleton  in  Birds 328 

CHAPTER   XX. 

Characters  of  the  several  groups  of  Mammalia      ....     343 

CHAPTER   XXI. 

The  skeleton  of  the  Dog  (Canis  familiaris) 374 

CHAPTER   XXII. 

General  account  of  the  skeleton  in  Mammalia.     The  exoskeleton 

and  vertebral  column        . .416 

CHAPTER   XXIII. 

General   account  of  the  skeleton  in  Mammalia  (continued}.     The 

skull  and  appendicular  skeleton 455 


LIST   OF   ILLUSTRATIONS. 


FIG.  PAGE 

1  Diagrammatic  sections  of  various  forms  of  teeth  ...  6 

2  Cervical  vertebrae  of  an  Ox  (Bos  taurus)       ....  15 

3  Diagram  of  the  skeleton  of  Amphioxus  lanceolatus        .         .  51 

4  Dorsal,   lateral,   and  ventral   views   of    the   skull   of   Petro- 

myzon  marinus 56 

5  Skull  of  a  male  Chimaera  monstrosa 65 

6  Lateral  view  of  the  skull  of  a  Dogfish  (Scyllium  canicula)  .  75 

7  Semidorsal  view  of  the  pectoral  girdle  and  fins  of  a  Dogfish 

(Scyllium  canicula)       . 80 

8  Dorsal  view  of  the  pelvic  girdle  and  fins  of  a  male  Dogfish 

(Scyllium  canicula) 81 

9  Dorsal  and  ventral  views  of  the  cranium  of  a  Salmon  (Salmo 

salar)  from  which  most  of  the  membrane  bones  have  been 

removed 88 

10  Lateral  view   of  the   chondrocranium   of  a  Salmon   (Salvio 

salar) 90 

11  Lateral  view  of  the  skull  of  a  Salmon  (Salmo  salar)   .         .  92 

12  Mandibular  and  hyoid  arches  of  a  Cod  (Gadus  morrhua)     .  99 

13  Eight  half  of  the  pectoral  girdle  and  right  pectoral  fin  of  a  Cod 

(Gadus  morrhua) 102 

14  Diagram  of  a  section  through  the  jaw  of  a  Shark  (Odontaspis 

americanus)  showing  the  succession  of  teeth      .         .         .  107 

15  Part  of  the  lower  jaw  of  a  Shark  (Galeus)    ....  108 

16  Skulls  of  Notidanus  and  Cestracion        .....  118 

17  Dorsal  view  of  the  branchial  arches  of  Heptanchus      .         .  120 

18  Lateral  view  of  the  skull  of  a  Sturgeon  (Acipenser  sturio)   .  122 

19  Dorsal  and  ventral  views  of  the  cranium  of  Ceratodus  miolepis  125 

20  Lateral  view  of  the  skeleton  of  Ceratodus  miolepis        .         .  128 

21  Dorsal,  ventral  and  lateral  views  of  the  skull  of  a  Newt  (Molge 

cristata) 142 

22  Ventral  and  lateral  views  of  the  shoulder-girdle  and  sternum 

of  an  old  male  Crested  Newt  (Molge  cristata)    .         .         .  146 


LIST   OF   ILLUSTRATIONS.  Xlll 

FIG.  PAOK 

23  Eight    posterior    and    anterior    limbs    of    a    Newt    (Molge 

cristata) 148 

24  Dorsal  and  ventral  views  of  the  cranium  of  a  Common  Frog 

(Rana  temporaria) 155 

25  Dorsal  and  ventral  views  of  the  cranium  of  a  Common  Frog 

(Rana  temporaria)  from  which  the  membrane  bones  have 
mostly  been  removed  .         .         .  • 157 

26  Lateral  view  of  the  skull  and  posterior  view  of  the  cranium  of 

a  Common  Frog  (Rana  temporaria) 159 

27  Dorsal  view  of  the  skull  of  a  Labyrinthodont  (Capitosaurus 

nasutus) 176 

28  Ventral  view  of  the  cranium,  and  lateral  view  of  the  cranium 

and  mandible  of  Siphonops  annulatus      ....         178 

29  Visceral  arches  of  Amphibia :    A,  Molge  cristata ;   B,   Rana 

temporaria,  adult;  C,  Tadpole  of  Rana;  D,  Siredon  pisci- 
formis 181 

30  Shoulder-girdle  and  sternum  of  an  adult  male  Common  Frog 

(Rana  temporaria),  and  of  an  adult  female  Docidophryne 
gigantea 183 

31  A,  Eight   antibrachium  and  manus  of  a  larval  Salamander 

(Salamandra    maculosa);    B,   Eight  tarsus  and   adjoining 
bones  of  Molge  sp 186 

32  Lateral  and  dorsal  views  of  the  skull  of  an  Ichthyosaurus  .     196 

33  Lateral  view  and  longitudinal  section  of  the  skull  of  a  Lizard 

(Varanus  varius)  .........  201 

34  Lateral  view  of  the  shoulder-girdle  of  a  Lizard  (Varanus)   .  202 

35  Eestored  skeleton  of  Ceratosaurus  nasicornis          .        .         .  206 

36  Dorsal  and  ventral  views  of  the  carapace  of  a  Loggerhead 

Turtle  (Thalassochelys  caretta) 216 

37  Plastron  of  a  Green  Turtle  (Ghelone  midas)  ....     218 

38  The  skull  of  a  Green  Turtle  (Ghelone  midas)        .         .         .223 

39  Longitudinal  vertical  section  through  the  cranium  of  a  Green 

Turtle  (Chelone  midas) 226 

40  Anterior  limb  of  a  young  Hawksbill  Turtle  (Chelone  imbri- 

cata),  and  posterior  limb  of  a  large  Green  Turtle  (Chelone 
midas) 234 

41  The  first  four  cervical  vertebrae  of  a  Crocodile  (Crocodilus 

vulgaris) 239 

42  Anterior  view  of  a  late  thoracic  and  the  first  sacral  vertebrae 

of  a  Crocodile  (Crocodilus  palustris) 242 


XIV  LIST   OF    ILLUSTRATIONS. 


43  Palatal  aspect  of  the  cranium  and  mandible  of  an  Alligator 

(Caiman  Jatirostris) 245 

44  Lateral  view  of  the  skull  of  an  Alligator  (Caiman  latirostris)   .     248 

45  Longitudinal  section  through  the  skull  of  an  Alligator  (Caiman 

latirostris) 253 

46  Sternum    and  associated   membrane  bones    of    a   Crocodile 

(Crocodilus  palustris) 261 

47  Left  half  of  the  pectoral   girdle   of    an   Alligator   (Caiman 

latirostris) 262 

48  Right  anterior  and  posterior  limbs  of  an  Alligator  (Caiman 

latirostris) 264 

49  Pelvis  and  sacrum  of  an  Alligator  (Caiman  latirostris)         .     267 

50  Preparation  of  part  of  the  right  mandibular  ramus  of  Croco- 

dilus palustris 274 

51  Dorsal  and  ventral  views  of  the  skull  of  a  Common  Snake 

(Tropidonotus  natrix) 279 

52  Skull  of  Hatteria  (Sphenodon  punctatus)         ....     282 

53  Hyoids  of  an  Alligator  (Caiman  latirostris),  and  of  a  Green 

Turtle  (Chelone  midas) 285 

54  Ventral  view  of  the  shoulder-girdle  and  sternum  of  Loemanctus 

longipes 287 

55  Left  half  of  the  skeleton  of  a  Common  Fowl  (Gallus  bankiva)     301 

56  The  wing  of  a  Wild  Duck  (Anas  boschas)      ....     304 

57  Wings   of   a  Wild   Duck   with   the   coverts  removed   (Anas 

bosc.has)         . 305 

58  Dorsal  and  ventral  views  of  the  pelvis  and  sacrum  of  a  Duck 

(Anas  boschas) 311 

59  Skull  of  a  Duck  (Anas  boschas) 312 

60  A,  Ventral  view  of  the  cranium  of  a  Duck  (Anas  boschas) ;  B, 

Cranium  and  mandible  seen  from  the  left  side          ,         .     313 

61  Lateral  view  of  the  pelvis  and  sacrum  of  a  Duck  (Anas  boschas)     325 

62  Third  cervical  vertebra  of  an  Ostrich  (Struthio  camelus)       .     331 

63  Shoulder-girdle   and  sternum   of  A,   Black  Vulture  (Vultur 

cinereus) ;  B,  Peacock  (Pavo  cristatus) ;  C,  Pelican  (Pelica- 

nus  conspicillatus) 337 

64  Bones  of  the  right  wing  of  A,    a   Penguin;    B,  an  Ostrich 

(Struthio  camelus)  and  C,  a  Gannet  (Sula  alba)    .         .         .     339 

65  Pelvic  girdle  and  sacrum  of  A,  Cassowary  (Casuarius  galeatus); 

B,  Owen's  Apteryx  (A.  oweni)-,   C,  Broad-billed  Rhea  (R. 
macrorhyncha) ;  D,  Ostrich  (Struthio  camelus)      .         .         .     340 


LIST   OF   ILLUSTRATIONS.  XV 

no.  PAGE 

66  Ventral  view  of  the  shoulder-girdle  and  sternum  of  a  Duckbill 

(Ornithorhynchus  paradoxus) 347 

67  Cervical  vertebrae  of  a  Ca'ing  Whale  (Globicephalus  mclas)  .  354 

68  Dentition  of  a  Dog  (Canis  familiar  is) 375 

69  Atlas  and  axis  vertebrae  of  a  Dog  (Canis  familiaris)    .         .  379 

70  Second  thoracic  and  second  lumbar  vertebrae  of  a  Dog  (Canis 

familiaris) 382 

71  Diagram  of  the  relations  of  the  principal  bones  in  the  Mamma- 

lian skull 385 

72  Vertical  longitudinal  section  through  skull  of  a  Dog  (Canis 

familiaris) 387 

73  Dorsal  view  of  the  cranium  of  a  Dog  (Canis  familiaris)    .         .  389 

74  Diagram  of  the  mammalian  tympanic  cavity  and  associated 

bones 391 

75  Ventral  view  of  the  cranium  of  a  Dog  (Canis  familiaris)  .         .  396 

76  Sternum  and  sternal  ribs  of  a  Dog  (Canis  familiaris)       .         .  403 

77  Bones  of  the  left  upper  arm  and  fore-arm  of  a  Dog  (Canis 

familiaris) 407 

78  Bight  innominate  bone,  A,  of  a  full-grown  Terrier ;  B,  of  a 

Collie  Puppy 410 

79  Left  leg  bones  of  a  Dog  (Canis  familiaris)         .         .         .         .411 

80  A,   Eight  manus;    B,   Eight  pes   of   a   Dog   (Cam's  famili- 

aris)        413 

81  Skull  of  a  young  Indian  Ehinoceros  (R.  unicornis)  showing  the 

change  of  the  dentition 421 

82  Palatal  aspect  of  the  cranium  and  mandible  of  a  Donkey  (Equus 

asinus) 431 

83  Skull  of  Procavia  (Dendrohyrax)  dorsalis       ....  433 

84  Carnassial  or  sectorial  teeth  of  Carnivora      .         .         .         .  436 

85  Mandible  of  Isabelline  Bear  (Ursus  isabellinus)     .         .        .  438 

86  Left    mandibular   ramus   of  the    Sea  Leopard   (Ogmorhinus 

leptonyx) 439 

87  Cervical    vertebrae    of    a    young   Fin    Whale    (Balaenoptera 

musculus) 444 

88  Atlas  and  axis  vertebrae  of  an  Ox  (Bos  taurm)    .        .         .  445 

89  First  and  second  thoracic  vertebrae  of  an  Ox  (Bos  taunts)  .  449 

90  Skulls  of  Tasmanian   Wolf   (Thylacinus  cynocephalus)    and 

Hairy-nosed  Wombat  (Phascolomys  latifrons)     .         .         .  456 

91  Skull  of  Two-fingered  Sloth  (Choloepus  didactylus)        .         .  458 

92  Skull  of  Rhytina  stelleri 460 


XVI  LIST   OF   ILLUSTRATIONS. 

FIG.  PAGE 

93  Lateral  view  and  longitudinal  section  of  the  skull  of  a  young 

Ca'ing  Whale  (Globicephahis  melas) 463 

94  Cranium  and  mandible  of  a  Pig  (Sus  scrofa)         .         .         .  466 

95  Mandible  of  a  Hippopotamus  (Hippopotamus  amphibius)       .  467 

96  Skull  of  a  young  Indian  Elephant  (Elephas  indicus)    .         .  474 

97  Longitudinal  section  of  the  skull  of  a  young  Indian  Elephant 

(Elephas  indicus) 475 

98  Half-front  view  of  the  skull  of  a  Porcupine  (Hystrix  cristata)  .     477 

99  Skulls  of  an  old  and  of  a  young  Gorilla  (Gorilla  savagei)  .     483 

100  Malleus,  stapes,  and  incus  of  Man,  Dog,  and  Eabbit    .         .     485 

101  Skeleton  of  a  Cape  Buffalo  (Bubalus  coffer)  .         .         .         .492 

102  Lateral  and  dorsal  views  of  the  shoulder-girdle  and  part  of 

the  sternum  of  the  Spiny  Anteater  (Echidna  aculeata)     .     494 

103  Skeleton  of  a  Llama  (Auchenia  glama)  ....     496 

104  Dorsal  view  of  the  sternum  and  right  half  of  the  shoulder- 

girdle  of  Mus  sylvaticus 498 

105  Anterior  surface  of  the  right  humerus  of  a  Wombat  (Phasco- 

lomys  latifrons) 500 

106  Manus  of  Perissodactyles :    A,  Left   manus  of   Tapirus ;    B, 

Right  manus  of  Titanotherium ;  C,  Left  manus  of  Chalico- 
therium  giganteum 508 

107  Left  manus  of  A,  Coryphodon  hamatus;   B,  Phenacodus  pri- 

maevus ;  C,  Procavia  (Dendrohyrax)  arboreus      .         .         .     510 

108  Left  anterior  and  posterior  limbs  and  limb  girdles  of  Uinta- 

therium  mirabile  .         . 516 

109  Left  femur  of  an  Ox  (Bos  taurus)  and  of  a  Sumatraii  Rhinoceros 

(Rhinoceros  sumatrensis)        .         .         .         .        .         .        .518 

110  Pes  of  A,  a  Tapir  (Tapirus   americanus) ;   B,  a   Rhinoceros 

(Rhinoceros  sumatrensis) ;  C,  Hipparion  gracile  ;  D,  a  Horse 
(Equus  caballus) 524 


ERRATA. 

p.  172,  note,  for  14  read  15. 

p.  279,  description  of  figure,  for  Tropidinotus  read  Tropidonotus. 
p.  287,  description   of   figure,  for   shoulder-girdle  of   sternum   read 

shoulder-girdle  and  sternum, 
p.  393,  middle  of  page,  for  VIII  read  VII. 
p.  427,  line  2,  for  Grampus  read  Killer. 


CHAPTER   I. 

INTRODUCTORY  ACCOUNT   OF  THE   SKELETON   IN 
GENERAL. 

BY  the  term  skeleton  is  meant  the  hard  structures  whose 
function  is  to  support  or  to  protect  the  softer  tissues  of  the 
animal  body. 

The  skeleton  is  divisible  into 

A.  The  EXOSKELETON,  which  is  external ; 

B.  The    ENDOSKELETON,    which   is   as   a    rule   internal ; 
though  in  some  cases,  e.g.  the  antlers  of  deer,  endoskeletal 
structures  become,  as  development  proceeds,  external. 

In  Invertebrates  the  hard,  supporting  structures  of  the 
body  are  mainly  exoskeletal,  in  Vertebrates  they  are  mainly 
endoskeletal ;  but  the  endoskeleton  includes,  especially  in 
the  skull,  a  number  of  elements,  the  dermal  or  membrane 
bones,  which  are  shown  by  development  to  have  been  originally 
of  external  origin.  These  membrane  bones  are  so  intimately 
related  to  the  true  endoskeleton  that  they  will  be  described 
with  it.  The  simplest  and  lowest  types  of  both  vertebrate 
and  invertebrate  animals  have  unsegmented  skeletons ;  with 
the  need  for  flexibility  however  segmentation  arose  both  in 
the  case  of  the  invertebrate  exoskeleton  and  the  vertebrate 
endoskeleton.  The  exoskeleton  in  vertebrates  is  phylogeneti- 
cally  older  than  the  endoskeleton,  as  is  indicated  by  both 
R.  1 


2  THE  VERTEBRATE  SKELETON. 

palaeontology  and  embryology.  Palaeontological  evidence  is 
afforded  by  the  fact  that  all  the  lower  groups  of  vertebrates — 
Fish,  Amphibia,  and  Reptiles — had  in  former  geological  periods 
a  greater  proportion  of  species  protected  by  well-developed 
dermal  armour  than  is  the  case  at  present.  Embryological 
evidence  tends  the  same  way,  inasmuch  as  dermal  ossifications 
appear  much  earlier  in  the  developing  animal  than  do  the 
ossifications  in  the  endoskeleton. 

Skeletal  structures  may  be  derived  from  each  of  the  three 
germinal  layers.  Thus  hairs  and  feathers  are  epiblastic  in 
origin,  bones  are  mesoblastic,  and  the  notochord  is  hypo- 
blastic. 

The  different  types  of  skeletal  structures  may  now  be  con- 
sidered and  classified  more  fully. 

A.       EXOSKELETAL    STRUCTURES. 

I.     EPIBLASTIC  (epidermal). 

Exoskeletal  structures  of  epiblastic  origin  may  be  developed 
on  both  the  inner  and  outer  surfaces  of  the  Malpighian  layer  of 
the  epidermis1.  Those  developed  on  the  outer  surface  include 
hairs,  feathers,  scales,  nails,  beaks  and  tortoiseshell;  and 
are  specially  found  in  vertebrates  higher  than  fishes.  Those 
developed  on  the  inner  surface  of  the  Malpighian  layer  include 
only  the  enamel  of  teeth  and  some  kinds  of  scales.  With 
the  exception  of  feathers,  which  are  partly  formed  from  the 
horny  layer,  all  these  parts  are  mainly  derived  from  the  Mal- 
pighian layer  of  the  epidermis. 

1  The  skin  consists  of  an  outer  layer  of  epiblastic  origin,  the 
epidermis,  and  an  inner  layer  of  mesoblastic  origin,  the  dermis.  The 
epidermis  is  divided  into  two  principal  layers,  an  outer  one,  the  horny 
layer  or  stratum  corneum,  and  an  inner  one,  the  stratum  Malpighii.  The 
innermost  part  of  the  stratum  corneum  is  distinguished  as  the  stratum 
lucidum,  and  the  outermost  part  of  the  stratum  Malpighii  as  the  stratum 
granulosum. 


INTRODUCTORY.      EPIBLASTIC   STRUCTURES.  3 

Hairs  are  slender,  elongated  structures  which  arise  by 
the  proliferation  of  cells  from  the  Malpighian  layer  of  the 
epidermis.  These  cells  in  the  case  of  each  hair  form  a  short 
papilla,  which  sinks  inwards  and  becomes  imbedded  at  the 
bottom  of  a  follicle  in  the  dermis.  Each  hair  is  normally 
composed  of  an  inner  cellular  pithy  portion  containing  much 
air,  and  an  outer  denser  cortical  portion  of  a  horny  nature. 
Sometimes,  as  in  Deer,  the  hair  is  mainly  formed  of  the  pithy 
portion,  and  is  then  easily  broken.  Sometimes  the  horny  part 
predominates,  as  in  the  bristles  of  Pigs.  A  highly  vascular 
dermal  papilla  projects  into  the  base  of  the  hair. 

Feathers,  like  hairs,  arise  from  epidermal  papillae  which 
become  imbedded  in  pits  in  the  dermis.  But  the  feather  germ 
differs  from  the  hair  germ,  in  the  fact  that  it  first  grows 
out  like  a  cone  on  the  surface  of  the  epidermis,  and  that 
the  horny  as  well  as  the  Malpighian  layer  takes  part  in  its 
formation. 

Nails,  claws,  hoofs,  and  the  horns  of  Oxen  are  also 
epidermal,  as  are  such  structures  as  the  scales  of  reptiles,  of 
birds'  feet,  and  of  Manis  among  mammals,  the  rattle  of  the 
rattlesnake,  the  nasal  horns  of  Rhinoceros,  and  the  baleen 
of  whales.  All  these  structures  will  be  described  later. 

Nails  arise  in  the  interior  of  the  epidermis  by  the  thicken- 
ing and  cornification  of  the  stratum  lucidum.  The  outer 
border  of  the  nail  soon  becomes  free,  and  growth  takes  place 
by  additions  to  the  inner  surface  and  attached  end. 

When  a  nail  tapers  to  a  sharp  point  it  is  called  a  claw. 
In  many  cases  the  nails  more  or  less  surround  the  ends  of 
the  digits  by  which  they  are  borne. 

Horny  beaks  of  epidermal  origin  occur  casing  the  jaw- 
bones in  several  widely  distinct  groups  of  animals.  Thus 
among  reptiles  they  are  found  in  Chelonia  (tortoises  and 
turtles)  as  well  as  in  some  extinct  forms ;  they  occur  in  all 
living  birds,  in  Ornithorhynchus  among  mammals,  and  in  the 
larvae  of  many  Amphibia. 

1—2 


4  THE  VERTEBRATE  SKELETON. 

In  a  few  animals,  such  as  Lampreys  and  Ornithorhynchus, 
the  jaws  bear  horny  tooth-like  structures  of  epidermal  origin. 

The  enamel  of  teeth  and  of  placoid  scales  is  also  epi- 
blastic  in  origin1,  and  it  may  be  well  at  this  point  to  give 
some  account  of  the  structure  of  teeth,  though  they  are 
partly  mesoblastic  in  origin.  The  simplest  teeth  are  those 
met  with  in  sharks  and  dogfish,  where  they  are  merely  the 
slightly  modified  scales  developed  in  the  integument  of  the 
mouth.  They  pass  by  quite  insensible  gradations  into  normal 
placoid  scales,  such  as  cover  the  general  surface  of  the  body. 
A  placoid  scale2  is  developed  on  a  papilla  of  the  dermis 
which  projects  outwards  and  backwards,  and  is  covered  by  the 
columnar  Malpighian  layer  of  the  epidermis.  The  outer  layer 
of  the  dermal  papilla  then  gradually  becomes  converted  into 
dentine  and  bone,  while  enamel  is  developed  on  the  inner  side 
of  the  Malpighian  layer,  forming  a  cap  to  the  scale.  The 
Malpighian  and  horny  layers  of  the  epidermis  get  rubbed  off 
the  enamel  cap,  so  that  it  comes  to  project  freely  on  the  sur- 
face of  the  body. 

As  regards  their  attachment  teeth  may  be  (1)  attached 
to  the  fibrous  integument  of  the  mouth,  or  (2)  fixed  to  the 
jaws  or  other  bones  of  the  mouth,  or  (3)  planted  in  grooves, 
or  (4)  in  definite  sockets  in  the  jaw-bones  (see  p.  107). 

Teeth  in  general  consist  of  three  tissues,  enamel,  dentine 
and  cement,  enclosing  a  central  pulp-cavity  containing  blood- 
vessels and  nerves.  Enamel  is,  however,  often  absent,  as  in  all 
living  Edentates. 

Enamel  generally  forms  the  outermost  layer  of  the  crown 
or  visible  part  of  the  tooth  ;  it  is  the  hardest  tissue  occurring 
in  the  animal  body  and  consists  of  prismatic  fibres  arranged  at 
right  angles  to  the  surface  of  the  tooth.  It  is  characterised  by 
its  bluish- white  translucent  appearance. 

1  The  enamel  of  the  pharyngeal  teeth  of  some  Teleosteans  is  hypo- 
blastic  in  origin. 

2  See  also  p.  71. 


INTRODUCTORY.      TEETH.  5 

II.     MESOBLASTIC  (mesodermal). 

Dentine  or  ivory  generally  forms  the  main  mass  of  a 
tooth.  It  is  a  hard,  white  substance  allied  to  bone.  When 
examined  microscopically  dentine  is  seen  to  be  traversed  by 
great  numbers  of  nearly  parallel  branching  tubules  which 
radiate  outwards  from  the  pulp-cavity.  In  fishes  as  a  rule, 
and  sometimes  in  other  animals,  a  variety  of  dentine  con- 
taining blood-vessels  occurs,  this  is  called  vasodentine. 

Cement  or  crusta  petrosa  forms  the  outermost  layer  of 
the  root  of  the  tooth.  In  composition  and  structure  it  is 
practically  identical  with  bone.  In  the  more  complicated 
mammalian  teeth,  besides  enveloping  the  root,  it  fills  up  the 
spaces  between  the  folds  of  the  enamel. 

The  hard  parts  of  a  tooth  commonly  enclose  a  central  pulp- 
cavity  into  which  projects  the  pulp,  a  papilla  of  the  dermis 
including  blood-vessels  and  nerves.  As  long  as  growth  con- 
tinues the  outer  layers  of  this  pulp  become  successively  calcified 
and  added  to  the  substance  of  the  dentine.  In  young  growing 
teeth  the  pulp-cavity  remains  widely  open,  but  in  mammals 
the  general  rule  is  that  as  a  tooth  gets  older  and  the  crown 
becomes  fully  formed,  the  remainder  of  the  pulp  becomes 
converted  into  one  or  more  tapering  roots  which  are  im- 
bedded in  the  alveolar  cavities  of  the  jaws.  The  opening  of 
the  pulp-cavity  is  then  reduced  to  a  minute  perforation  at  the 
base  of  each  root.  A  tooth  of  this  kind  is  called  a  rooted 
tooth. 

But  it  is  not  only  in  young  teeth  that  the  pulp-cavity 
sometimes  remains  widely  open;  for  some  teeth,  such  as  the 
tusks  of  Elephants  and  the  incisor  teeth  of  Rodents,  form 
no  roots  and  continue  to  grow  throughout  the  animal's 
life.  Such  teeth  are  said  to  be  rootless  or  to  have  persistent 
pulps. 

An  intermediate  condition  is  seen  in  some  teeth,  such  as 
the  grinding  teeth  of  Horses  These  teeth  grow  for  a  very 
long  time,  their  crowns  wearing  away  as  fast  as  their  bases 


THE  VERTEBRATE  SKELETON. 


FIG.  1.     DIAGRAMMATIC  SECTIONS  OF  VARIOUS  FORMS  OF  TEETH 
(from  FLOWER). 

I.  Incisor  or  tusk  of  elephant,  with  pulp-cavity  persistently  open  at 
base.  II.  Human  incisor  during  development  with  root  imperfectly 
formed,  and  pulp-cavity  widely  open  at  base.  III.  Completely  formed 
human  incisor,  with  pulp-cavity  contracted  to  a  small  aperture  at  the 
end  of  the  root.  IV.  Human  molar  with  broad  crown  and  two  roots. 
V.  Molar  of  Ox,  with  the  enamel  covering  the  crown,  deeply  folded  and 
the  depressions  filled  with  cement.  The  surface  is  worn  by  use,  other- 
wise the  enamel  coating  would  be  continuous  at  the  top  of  the  ridges. 
In  all  the  figures  the  enamel  is  black,  the  pulp  white,  the  dentine 
represented  by  horizontal  lines,  and  the  cement  by  dots. 


INTRODUCTORY.      TEETH.  7 

are  produced;  finally  however  definite  roots  are  formed  and 
growth  ceases. 

The  teeth  of  any  animal  may  be  homodont,  that  is,  all 
having  the  same  general  character,  or  heterodont,  that  is, 
having  different  forms  adapted  to  different  functions.  The 
dentition  is  heterodont  in  a  few  reptiles  and  the  majority  of 
mammals. 

SUCCESSION  OF  TEETH.  In  most  fishes,  and  many  amphibians 
and  reptiles  the  teeth  can  be  renewed  indefinitely.  In  sharks, 
for  example,  numerous  rows  of  reserve  teeth  are  to  be  seen 
folded  back  behind  those  in  use  (see  fig.  15).  The  majority  of 
mammals  have  only  two  sets  of  teeth,  and  are  said  to  be  diphy- 
odont ;  some  have  only  a  single  series  (monophyodont). 

DEVELOPMENT  OF  TEETH.  A  brief  sketch  of  the  method  in 
which  development  of  teeth  takes  place  in  the  higher  verte- 
brates may  here  be  given.  Along  the  surface  of  the  jaws  a 
thickening  of  the  epiblastic  epithelium  takes  place,  giving  rise 
to  a  ridge,  which  sinks  inwards  into  the  tissue  of  the  jaw, 
and  it  is  known  as  the  primary  enamel  organ.  At  the  points 
where  teeth  are  to  be  developed  special  ingrowths  of  this 
primary  enamel  organ  take  place,  and  into  each  there  projects 
a  vascular  dental  papilla  from  the  surrounding  mesoblast  of 
the  jaw.  Each  ingrowth  of  the  enamel  organ  forms  an 
enamel  cap,  which  gradually  embraces  the  dental  papilla, 
and  at  the  same  time  appears  to  be  pushed  on  one  side,  owing 
to  the  growth  not  being  uniform.  The  external  layer  of 
the  dental  papilla  is  composed  of  long  nucleated  cells,  the 
odontoblasts,  and  it  is  by  these  that  the  dentine  is  formed. 
Similarly  the  internal  layer  of  the  enamel  organ  is  formed  of 
columnar  enamel  cells,  which  give  rise  to  the  enamel.  The 
mesoblastic  cells  surrounding  the  base  of  the  tooth  give  rise 
to  the  cement. 

Bone  is  in  many  cases  exoskeletal,  but  it  will  be  most 
conveniently  described  with  the  endoskeleton. 


8  THE  VERTEBRATE  SKELETON. 

The  scales  of  fish  are  wholly  or  in  part  mesoblastic 
in  origin,  being  totally  different  from  those  of  reptiles.  The 
cycloid  and  ctenoid  scales  of  Teleosteans  (see  p.  105)  are  thin 
plates  coated  with  epidermis.  They  are  sometimes  bony,  but 
as  a  rule  are  simply  calcified.  Ganoid  scales  are  flat  plates 
of  bone  coated  with  an  enamel-like  substance,  and  articulating 
together  with  a  peg  and  socket  arrangement;  they  are  pro- 
bably identical  with  enlarged  and  flattened  placoid  scales. 

The  armour  plates  of  fossil  Ganoids,  Labyrinthodonts, 
and  Dinosaurs,  and  of  living  Crocodiles,  some  Lizards  and 
Armadillos,  are  composed  of  bone.  They  are  always  covered 
by  a  layer  of  epidermis. 

The  antlers  of  deer  are  also  composed  of  bone ;  they 
will  be  more  fully  described  in  the  chapter  on  mammals. 
It  may  perhaps  be  well  to  mention  them  here,  though  they 
really  belong  to  the  endoskeleton,  being  outgrowths  from  the 
frontal  bones. 

B.     ENDOSKELETAL  STRUCTURES. 
I.     HYPOBLASTIC. 

(a)  The    notochord  is    an   elastic  rod   formed  of  large 
vacuolated  cells,  and  is  surrounded  by  a  membranous  sheath 
of  mesoblastic  origin.      It  is  the  primitive   endoskeleton  in 
the  Chordata,  all  of  which  possess  it  at  some  period  of  their 
existence;  while  in  many  of  the  lower  forms  it  persists  through- 
out life.     Even  in  the  highest  Chordata  it  is  the  sole  repre- 
sentative of  the  axial  skeleton  for  a  considerable  part  of  the 
early    embryonic    life.       A    simple    unsegmented    notochord 
persists  throughout  life  in  the  Cephalochordata,  Cyclostomata, 
and  some  Pisces,  such  as  Sturgeons  and  Chimaeroids. 

(b)  The  enamel  of  the  pharyngeal   teeth  of  the  Salmon 
and  many  other  Teleosteans  is  hypoblastic  in   origin.     The 
epiblast    of   the    stomodaeum,  in  which   the   other  teeth    are 
developed,  passes  into   the    hypoblast    of  the   mesenteron  in 
which  these  pharyngeal  teeth  are  formed. 


INTRODUCTORY.      BONE.  9 

II.     MESOBLASTIC. 

The  most  primitive  type  of  a  mesoblastic  endoskeleton 
consists  of  a  membranous  sheath  surrounding  the  notochord, 
as  in  Myxine  and  its  allies.  The  first  stage  of  complication 
is  by  the  development  of  cartilage  in  the  notochordal  sheath, 
as  in  Petromyzon.  Often  the  cartilage  becomes  calcified  in 
places,  as  in  the  vertebral  centra  of  Scyllium  and  other  Elas- 
mobranchs.  Lastly,  the  formation  of  bone  takes  place ;  it 
generally  constitutes  the  most  important  of  the  endoskeletal 
structures. 

Bone  may  be  formed  in  two  ways  : — 

(1)  by   the   direct    ossification  of   pre-existing  cartilage, 
when  it  is  known  as  cartilage  bone  or  endochondral  bone ; 

(2)  by  independent  ossification  in  connective  tissue  ;  it  is 
then  known  as  membrane  or  dermal  or  periosteal  bone. 

With  the  exception  of  the  clavicle1  all  the  bones  of  the  trunk 
and  limbs,  together  with  a  large  proportion  of  those  of  the 
skull,  are  preformed  in  the  embryo  in  cartilage,  and  are  grouped 
as  cartilage  bones  :  while  the  clavicle  and  most  of  the  roofing 
and  jaw-bones  of  the  skull  are  not  preformed  in  cartilage,  being 
developed  simply  in  connection  with  a  membrane.  Hence  it 
is  customary  to  draw  a  very  strong  line  of  distinction  between 
these  two  kinds  of  bone;  in  reality  however  this  distinction 
is  often  exaggerated,  and  the  two  kinds  pass  into  one  another, 
and  as  will  be  shown  immediately,  the  permanent  osseous 
tissue  of  many  of  those  which  are  generally  regarded  as 
typical  cartilage  bones,  is  really  to  a  great  extent  of  periosteal 
origin.  The  palatine  bone,  for  instance,  of  the  higher  verte- 
brates in  general  is  preceded  by  a  cartilaginous  bar,  but  is 
itself  almost  entirely  a  membrane  bone. 

Before  describing  the  development  of  bone  it  will  be  well 
to  briefly  describe  the  structure  of  adult  bone  and  cartilage. 

1  It  is  usual  to  regard  the  clavicle  as  a  membrane  bone,  but  Kolliker 
has  shown  that  in  rabbit  embryos  of  about  the  17th  day  it  is  cartilaginous. 


10  THE  VERTEBRATE  SKELETON. 

The  commonest  kind  of  cartilage,  and  that  which  pre- 
forms so  many  of  the  bones  of  the  embryo,  is  hyaline  cartilage. 
It  consists  of  oval  nucleated  cells  occupying  cavities  (lacunae) 
in  a  clear  intercellular  semitransparent  matrix,  which  is  pro- 
bably secreted  by  the  cells.  Sometimes  one  cell  is  seen  in  each 
lacuna,  sometimes  shortly  after  cell-division  a  lacuna  may  con- 
tain two  or  more  cells.  The  free  surface  of  the  cartilage 
is  invested  by  a  fibrous  membrane,  the  perichondrium. 

Bone  consists  of  a  series  of  lamellae  of  ossified  substance 
between  which  are  oval  spaces,  the  lacunae,  giving  rise  to 
numerous  fine  channels,  the  canaliculi,  which  radiate  off  in 
all  directions.  The  lacunae  are  occupied  by  the  bone  cells 
which  correspond  to  cartilage  cells,  from  which  if  the  bone  is 
young,  processes  pass  off  into  the  canaliculi.  It  is  obvious 
that  the  ossified  substance  of  bone  is  intercellular  in  character, 
and  corresponds  to  the  matrix  of  cartilage. 

Bone  may  be  compact,  or  loose  and  spongy  in  character, 
when  it  is  known  as  cancellous  bone.  In  compact  bone 
many  of  the  lamellae  are  arranged  concentrically  round 
cavities,  the  Haversian  canals,  which  in  life  are  occupied  by 
blood-vessels.  Each  Haversian  canal  with  its  lamellae  forms 
a  Haversian  system.  In  spongy  bone  instead  of  Haversian 
canals  there  occur  large  irregular  spaces  filled  with  marrow, 
which  consists  chiefly  of  blood-vessels  and  fatty  tissue.  The 
centre  of  a  long  bone  is  generally  occupied  by  one  large  con- 
tinuous marrow  cavity.  The  whole  bone  is  surrounded  by 
a  fibrous  connective  tissue  membrane,  the  periosteum. 

THE  DEVELOPMENT  OF  BONE. 

Periosteal  ossification.  An  example  of  a  bone  en- 
tirely formed  in  this  way  is  afforded  by  the  parietal.  The 
first  trace  of  ossification  is  shown  by  the  appearance,  below 
the  membrane  which  occupies  the  place  of  the  bone  in  the 
early  embryo,  of  calcareous  spicules  of  bony  matter,  which 
are  laid  down  round  themselves  by  certain  large  cells,  the 


INTRODUCTORY.      DEVELOPMENT   OF   BONE.  11 

osteoblasts.  These  osteoblasts  gradually  get  surrounded  by 
the  matter  which  they  secrete  and  become  converted  into  bone 
cells,  arid  in  this  way  a  mass  of  spongy  bone  is  gradually  pro- 
duced. Meanwhile  a  definite  periosteum  has  been  formed  round 
the  developing  bone,  and  on  its  inner  side  fresh  osteoblasts 
are  produced,  and  these  with  the  others  gradually  render  the 
bone  larger  and  more  and  more  compact.  Finally,  the  middle 
layer  of  the  bone  becomes  again  hollowed  out  and  rendered 
spongy  by  the  absorption  of  part  of  the  bony  matter. 

Endochondral  ossification1.  This  is  best  studied  in  the 
case  of  a  long  bone  like  the  femur  or  humerus.  Such  a  long 
bone  consists  of  a  shaft,  which  forms  the  main  part,  and  two 
terminal  portions,  which  form  the  epiphyses,  or  portions 
ossifying  from  centres  distinct  from  that  forming  the  shaft  or 
main  part  of  the  bone. 

In  the  earliest  stage  the  future  bone  consists  of  hyaline 
cartilage  surrounded  by  a  vascular  sheath,  the  perichondrium. 

Then,  starting  from  the  centre,  the  cartilage  becomes  per- 
meated by  a  number  of  channels  into  which  pass  vessels  from 
the  perichondrium  and  osteoblasts.  In  this  way  the  centre 
of  the  developing  shaft  becomes  converted  into  a  mass  of 
cavities  separated  by  bands  or  trabeculae  of  cartilage.  This 
cartilage  next  becomes  calcified,  but  as  yet  is  not  converted 
into  true  bone.  The  osteoblasts  in  connection  with  the 
cavities  now  begin  to  deposit  true  endochondral  spongy  bone, 
and  then  after  a  time  this  becomes  absorbed  by  certain 
large  cells,  the  osteoclasts,  and  resolved  into  marrow  or  vas- 
cular tissue  loaded  with  fat.  So  that  the  centre  of  the  shaft 
passes  from  the  condition  of  hyaline  cartilage  to  that  of 
calcined  cartilage,  thence  to  the  condition  of  spongy  bone,  and 
finally  to  that  of  marrow.  At  the  same  time  beneath  the 

1  In  compiling  these  paragraphs  on  Histology,  free  use  has  been 
made  of  Klein  and  Noble  Smith's  Atlas  of  Histology,  the  small  Histo- 
logies of  Klein  and  Schafer,  Huxley's  Elementary  Physiology,  and  Lloyd 
Morgan's  Animal  Biology. 


12  THE  VERTEBRATE  SKELETON. 

perichondrium  osteoblasts  are  developed  which  also  begin  to 
give  rise  to  spongy  bone.  The  perichondrium  thus  becomes 
the  periosteum,  and  the  bone  produced  by  it,  is  periosteal  or 
membrane  bone.  So  that  while  a  continuous  marrow  cavity  is 
gradually  being  formed  in  the  centre  of  the  shaft,  the  layer  of 
periosteal  bone  round  the  margin  is  gradually  thickening,  and 
becoming  more  and  more  compact  by  the  narrowing  down  of  its 
cavities  to  the  size  of  Haversian  canals.  The  absorption  of 
endochondral  and  formation  of  periosteal  bone  goes  on,  till 
in  time  it  comes  about  that  the  whole  of  the  shaft,  except 
its  terminations,  is  of  periosteal  origin.  At  the  extremities 
of  the  shaft,  however,  and  at  the  epiphyses,  each  of  which 
is  for  a  long  time  separated  from  the  shaft  by  a  pad  of 
cartilage,  the  ossification  is  mainly  endochondral,  the  peri- 
osteal bone  being  represented  only  by  a  thin  layer. 

Until  the  adult  condition  is  reached  and  growth  ceases,  the 
pad  of  cartilage  between  the  epiphysis  and  the  shaft  continues 
to  grow,  its  outer  (epiphysial)  half  growing  by  the  formation  of 
fresh  cartilage  as  fast  as  its  inner  half  is  encroached  on  by  the 
growth  of  bone  from  the  shaft.  The  terminal  or  articular 
surfaces  of  the  bone  remain  throughout  life  covered  by  layers 
of  articular  cartilage. 

Even  after  the  adult  condition  is  reached  the  bone  is 
subject  to  continual  change,  processes  of  absorption  and  fresh 
formation  going  on  for  a  time  and  tending  to  render  the  bone 
more  compact. 

METHODS  IN  WHICH  BONES  ARE  UNITED  TO  ONE  ANOTHER. 

The  various  bones  composing  the  endoskeleton  are  united 
to  one  another  either  by  sutures  or  by  movable  joints. 

When  two  bones  are  suturally  united,  their  edges  fit 
closely  together  and  often  interlock,  being  also  bound  together 
by  the  periosteum. 

In  many  cases  this  sutural  union  passes  into  fusion  or 
ankylosis,  ossification  extending  completely  from  one  bone  to 


INTRODUCTORY.      JOINTS.  13 

the  other  with  the  obliteration  of  the  intervening  suture.  This 
feature  is  especially  well  marked  in  the  cranium  of  most  birds. 

The  various  kinds  of  joints  or  articulations1  may  be  sub- 
divided into  imperfect  joints  and  perfect  joints. 

In  imperfect  joints,  such  as  the  in tervertebral  joints  of 
mammals,  the  two  contiguous  surfaces  are  united  by  a  mass 
of  fibrous  tissue  which  allows  only  a  limited  amount  of  motion. 

In  perfect  joints  the  contiguous  articular  surfaces  are 
covered  with  cartilage,  and  between  them  lies  a  synovial 
membrane  which  secretes  a  viscid  lubricating  fluid. 

The  amount  of  motion  possible  varies  according  to  the 
nature  of  the  articular  surfaces  ;  these  include — 

a.  ball  and  socket  joints,  like  the  hip  and  shoulder,  in 
which  the  end  of  one  bone  works  in  a  cup  provided  by  an- 
other, and  movements  can  take  place  in  a  variety  of  planes. 

b.  hinge  joints,  like  the  elbow  and  knee,  in  which  as 
in  ball-and-socket  joints  one  bone  works  in  a   cup  provided 
by  another,  but  movements  can  take  place  in  one  plane  only. 

THE  ENDOSKELETON. 

The  endoskeleton  is  divisible  into  axial  and  appendi- 
cular  parts ;  and  the  axial  skeleton  into — 

1.  the  spinal  column, 

(a.    the  cranium, 

2.  the  skull  {...,,.  .          111  + 

[o.    the  jaws  and  visceral  skeleton, 

3.  the  ribs  and  sternum2. 

I.     THE  AXIAL  SKELETON. 

1.     THE  SPINAL  COLUMN. 

The  spinal  column  in  the  simplest  cases  consists  of   an 

1  See  Huxley's  Elementary  Physiology,  Revised  edition,  London,  1886, 
p.  180. 

2  Strictly  speaking  the  jaws,  visceral  skeleton,  ribs  and  sternum  do 
not  form  part  of  the  axis,  but  it  is  convenient  to  group  them  as  parts  of 
the  axial  skeleton. 


14  THE  VERTEBRATE  SKELETON. 

unsegmented  rod,  the  notochord,  surrounded  by  the  skeleto- 
genous  layer,  a  sheath  of  mesoblastic  origin,  which  also 
envelops  the  nerve  cord.  Several  intermediate  stages  connect 
this  simple  spinal  column  with  the  vertebral  column  charac- 
teristic of  higher  vertebrates.  A  typical  vertebral  column 
may  be  said  to  consist  of  (1)  a  series  of  cartilaginous  or  bony 
blocks,  the  vertebral  centra,  which  arise  in  the  sheath 
surrounding  the  notochord.  They  cause  the  notochord  to 
become  constricted  and  to  atrophy  to  a  varying  extent,  though 
a  remnant  of  it  persists,  either  permanently  or  for  a  long 
period,  within  each  centrum  or  between  successive  centra. 
(2)  From  the  dorsal  surface  of  each  centrum  arise  a  pair  of 
processes  which  grow  round  the  spinal  cord  and  unite  above 
it,  forming  a  dorsal  or  neural  arch.  (3)  A  similar  pair 
of  processes  arising  from  the  ventral  surface  of  the  centrum 
form  the  ventral  or  haemal  arch.  To  the  ventral  arch 
the  ribs  strictly  belong,  and  it  tends  to  surround  the  ventral 
blood-vessels  and  the  body  cavity  with  the  alimentary  canal 
and  other  viscera. 

A  neural  spine  or  spinous  process  commonly  projects 
upwards  from  the  dorsal  surface  of  the  neural  arch,  and  a  pair 
of  transverse  processes  project  outwards  from  its  sides. 
When,  as  is  commonly  the  case,  the  two  halves  of  the  haemal 
arch  do  not  meet,  the  ventral  surface  of  the  centrum  often 
bears  a  downwardly-projecting  hypapophysis. 

The  character  of  the  surfaces  by  which  vertebral  centra 
articulate  with  one  another  varies  much.  Sometimes  both 
surfaces  are  concave,  and  the  vertebra  is  then  said  to  be 
amphicoelous ;  sometimes  a  centrum  is  convex  in  front  and 
concave  behind,  the  vertebra  is  then  opisthocoelous,  some- 
times concave  in  front  and  convex  behind,  when  the  vertebra 
is  procoelous.  Again,  in  many  vertebrae  both  faces  of  the 
centra  are  Hat,  while  in  others  they  are  saddle- shaped,  as  in  the 
neck  vertebrae  of  living  birds,  or  biconvex,  as  in  the  case  of 
the  first  caudal  vertebra  of  crocodiles. 


INTRODUCTORY.      VERTEBRAE. 


15 


In    the    higher   vertebrates    pads   of   fibro-cartilage — the 
intervertebral    discs — are   commonly    interposed    between 


2-- 


10 


FIG.  2.     CERVICAL  VERTEBRAE  OF  AN  Ox  (Bos  taunts). 


A,  is  the  fifth;   B,  the  fourth 

1.  neural  spine. 

2.  transverse  process. 

3.  hypapophysis. 

4.  convex  anterior  face  of  the 

centrum. 

5.  concave  posterior  face  of  the 

centrum. 


C,  the  third.  x£  (Camb.  Mus.) 

6.  prezygapophysis. 

7.  postzygapophysis. 

8.  vertebrarterial  canal. 

9.  neural  canal. 

10.     inferior  lamella  of  transverse 
process. 


successive  centra,  these  or  parts  of  them  often  ossify,  especially 
in  the  trunk  and  tail,  and  are  then  known  as  intercentra. 

The  vertebrae  of  the  higher  forms  can  generally  be  arranged 
in  the  following  five  groups,  each  marked  by  certain  special 
characteristics  : 

1.  The  cervical  or  neck  vertebrae.  These  connect 
the  skull  with  the  thorax,  and  are  characterised  by  relatively 
great  freedom  of  movement.  They  often  bear  small  ribs,  but 
are  distinguished  from  the  succeeding  thoracic  vertebrae  by 
the  fact  that  their  ribs  do  not  reach  the  sternum.  The  first 
cervical  vertebra  which  articulates  with  the  skull  is  called 
the  atlas,  but  a  study  of  the  nerve  exits  shows  that  the  first 


16  THE  VERTEBRATE  SKELETON. 

vertebra  is  not  serially  homologous  throughout  the  Ichthy- 
opsida,  so  that  it  is  best  to  reserve  the  term  atlas  for  the  first 
vertebra  in  Sauropsida  and  Mammalia. 

2.  The   thoracic  vertebrae  (often  called  dorsal)  bear 
movably    articulated    ribs    which    unite    ventrally    with    the 
sternum. 

3.  The  lumbar  vertebrae  are  generally  large,  and  are 
often  more  movable  on  one  another  than   are   the   thoracic 
vertebrae.     They  bear  no  ribs. 

4.  The  sacral  vertebrae  are  characterised  by  the  fact 
that  they  are  firmly  fused  together,  and  are  united  with  the 
pelvic  girdle  by  means  of  their  transverse  processes  and  rudi- 
mentary ribs. 

5.  The   caudal   or   tail  vertebrae   succeed  the  sacral. 
The  anterior  ones  are  often  fused  with  one  another  and  with 
the  sacrals,  but  they  differ  from  true  sacral  vertebrae  in  that 
there  are  no  rudimentary  ribs  between  their  transverse  pro- 
cesses   and    the   pelvic    girdle.      They    often    bear    V-shaped 
.chevron  bones. 

In  fish  and  snakes  the  vertebral  column  is  divisible  into 
only  two  regions,  an  anterior  trunk  region,  whose  vertebrae  bear 
ribs,  and  a  posterior  tail  region,  whose  vertebrae  are  ribless. 

2.     THE  SKULL. 

Before  giving  a  general  account  of  the  adult  skull  it  will 
be  well  to  briefly  describe  its  development. 

GENERAL  DEVELOPMENT  OF  THE  CRANIUM*. 

Shortly  after  its  appearance,  the  central  nervous  system 
becomes  surrounded  by  a  membranous  mesodermal  investment 
which  in  the  region  of  the  spinal  cord  is  called  the  skeleto- 
genous  layer  or  perichordal  sheath,  while  in  the  region 

1  F.  M.  Balfour,  Comparative  Embryology,  vol.  n.,  London,  1881, 
p.  465.  W.  K.  Parker  and  G.  T.  Bettany,  The  Morphology  of  the  Skull, 
London,  1877. 


INTRODUCTORY.      DEVELOPMENT   OF   THE    CRANIUM.     17 

of  the  brain  it  is  called  the  membranous  cranium.  Ventral 
to  the  central  nervous  system  is  the  notochord,  which  extends 
far  into  the  region  of  the  future  cranium,  and  like  the 
nervous  system,  is  enclosed  by  the  skeletogenous  layer.  The 
primitive  cartilaginous  cranium  is  formed  by  histological 
differentiation  within  the  substance  of  the  membranous 
cranium  and  always  consists  of  the  following  parts : 

(a)  the  parachordals.  These  are  a  pair  of  flat  curved 
plates  of  cartilage,  each  of  which  has  its  inner  edge  grooved 
where  it  comes  in  contact  with  the  notochord.  The  para- 
chordals, together  with  the  notochord,  form  a  continuous 
plate,  which  is  known  as  the  basilar  plate.  The  basilar 
plate  is  the  primitive  floor  below  the  hind-  and  mid-brain. 
In  front  the  parachordals  abut  upon  another  pair  of  carti- 
laginous bars,  the  trabeculae,  the  two  pairs  of  structures  being 
sometimes  continuous  with  one  another  from  the  first ; 

(6)  the  trabeculae  which  meet  behind  and  embrace  the 
front  end  of  the  notochord.  Further  forwards  they  at  first 
diverge  from  one  another,  and  then  converge  again,  enclosing 
a  space,  the  pituitary  space.  After  a  time  they  generally 
fuse  with  one  another  in  the  middle  line,  and,  with  the  para- 
chordals behind,  form  an  almost  continuous  basal  plate.  The 
trabeculae  generally  appear  before  the  parachordals.  They 
form  the  primitive  floor  below  the  fore-brain  ; 

(c)  the  cartilaginous  capsules  of  the  three  pairs  of  sense 
organs.  At  a  very  early  stage  of  development  involutions 
of  the  surface  epiblast  give  rise  to  the  three  pairs  of  special 
sense  organs — the  olfactory  or  nasal  organs  in  front,  the  optic 
in  the  middle,  and  the  auditory  behind.  The  olfactory  and 
auditory  organs  always  become  enclosed  in  definite  cartilagi- 
nous capsules,  the  eyes  often  as  in  the  Salmon,  become 
enclosed  in  cartilaginous  sclerotic  capsules,  while  sometimes, 
as  in  mammals,  their  protecting  capsules  are  fibrous. 

Each  pair  of  sense  capsules  comes  into  relation  with  part 
R.  2 


18  THE  VERTEBRATE  SKELETON. 

of  the  primitive  cranium,  and  greatly  modifies  it.  Thus  the 
auditory  or  periotic  capsules  press  on  the  parachordals  till 
they  come  to  be  more  or  less  imbedded  in  them.  Perhaps 
owing  to  the  pressure  of  the  nasal  capsules  the  trabeculae 
fuse  in  front,  and  then  grow  out  into  an  anterior  pair  of 
processes,  the  cornua  trabeculae,  and  a  posterior  pair,  the 
antorbital  processes,  which  together  almost  completely  sur- 
round the  nasal  capsules.  The  sclerotic  capsules  of  the  eyes 
greatly  modify  the  cranium,  although  they  never  become 
completely  united  with  it. 

The  cartilaginous  cranium  formed  of  the  basal  plate,  to- 
gether with  the  sense  capsules,  does  not  long  remain  merely 
as  a  floor.  Its  sides  grow  vertically  upwards,  forming  the 
exoccipital  region  of  the  cranium  behind,  and  the  ali- 
sphenoidal  and  orbitosphenoidal  regions  further  forwards. 
In  many  forms,  such  as  Elasmobranchs,  all  these  upgrowths 
meet  round  the  brain,  roofing  it  in  and  forming  an  almost 
complete  cartilaginous  cranium.  But  in  most  vertebrata, 
while  in  the  occipital  region,  the  cartilaginous  cranium  is 
completed  dorsally,  in  the  alisphenoidal  and  orbitosphenoidal 
regions  the  cartilage  merely  forms  the  lateral  walls  of  the 
cranium,  the  greater  part  of  the  brain  having  dorsal  to  it  a 
wide  space,  closed  by  merely  membranous  tissue  in  connection 
with  which  the  large  frontal  and  parietal  bones  are  subse- 
quently formed. 

The  SKULL  includes 

a.  the  cranium, 

b.  the  jaws  and  visceral  skeleton. 

The  cranium  can  be  further  subdivided  into 

(1)  an   axial  portion,  the  cranium  proper  or   brain 
case; 

(2)  the  sense  capsules.     The  capsules  of  the  auditory 
and  olfactory  sense  organs  are  always  present,  and  as  has  been 


INTRODUCTORY.   THE  CRANIUM.          19 

already   mentioned,    in    many    animals    the    eye   likewise    is 
included  in  a  cartilaginous  capsule. 

(1)      THE    CRANIUM    PROPER    Or    BRAIN    CASE. 

The  cranium  varies  much  in  form  and  structure.  In  lower 
vertebrates,  such  as  Sharks  and  Lampreys,  it  remains  entirely 
cartilaginous  and  membranous,  retaining  throughout  life  much 
of  the  character  of  the  embryonic  rudiment  of  the  cranium  of 
higher  forms.  The  dogfish's  cranium,  described  on  pp.  73  to 
76,  is  a  good  instance  of  a  cranium  of  this  type.  But  in  the 
majority  of  vertebrates  the  cartilage  becomes  more  or  less 
replaced  by  cartilage  bone,  while  membrane  bones  are  also 
largely  developed  and  supplant  the  cartilage. 

The  cranium  of  most  vertebrates  includes  a  very  large 
number  of  bones  whose  arrangement  varies  much,  but  one 
can  distinguish  a  definite  basicranial  axis  formed  of  the 
basi-occipital,  basisphenoid,  and  presphenoid  bones,  which  is 
a  continuation  forwards  of  the  axis  of  the  vertebral  column. 
From  the  basicranial  axis  a  wide  arch  arises,  composed  of  a 
number  of  bones,  which  form  the  sides  and  roof  of  the  brain- 
case.  These  bones  are  arranged  in  such  a  manner  that  if  both 
cartilage  and  membrane  bones  are  included  they  can  be  divided 
into  three  rings  or  segments.  The  hinder  one  of  these  seg- 
ments is  the  occipital,  the  middle  the  parietal,  and  the  anterior 
one  the  frontal. 

The  occipital  segment  is  formed  of  four  cartilage,  bones,  the 
basi-occipital  below,  two  exoccipitals  at  the  sides,  and  the 
supra-occipital  above.  The  parietal  segment  is  formed  of 
the  basisphenoid  below,  two  alisphenoids  at  the  sides  and 
two  membrane  bones,  the  parietals  above,  and  the  frontal 
segment  in  like  manner  consists  of  the  presphenoid  below, 
the  two  orbitosphenoids  at  the  sides,  and  two  membrane 
bones,  the  frontals,  above.  The  parietals  and  frontals,  being 
membrane  bones,  are  not  comparable  to  the  supra-occipital, 
in  the  way  that  the  presphenoid  and  basisphenoid  are  to  the 
basi-occipital. 

2—2 


20  THE  VERTEBRATE  SKELETON. 

The  cartilage  bones  of  the  occipital  segments  are  derived 
from  the  parachordals  of  the  embryonic  skull,  those  of  the 
parietal  and  frontal  segments  from  the  trabeculae. 

In  front  of  the  presphenoid  the  basicranial  axis  is  con- 
tinued by  the  mesethmoid. 

(2)    THE  SENSE  CAPSULES. 

These  enclose  and  protect  the  special  sense  organs. 

(a)  Auditory  capsule. 

The  basisphenoid  is  always  continuous  with  the  basi- 
occipital,  but  the  alisphenoid  is  not  continuous  with  the  ex- 
occipital  as  the  periotic  or  auditory  capsule  is  interposed 
between  them.  Each  periotic  capsule  has  three  principal 
ossifications  ;  an  anterior  bone,  the  pro-otic,  a  posterior  boner 
the  opisthotic,  and  a  superior  bone,  the  epi-otic. 

These  bones  may  severally  unite,  or  instead  of  uniting 
with  one  another  they  may  unite  with  the  neighbouring  bones. 
Thus  the  epi-otic  often  unites  with  the  supra-occipital,  and  the 
opisthotic  with  the  exoccipital. 

Two  other  bones  developed  in  the  walls  of  the  auditory 
capsule  are  sometimes  added,  as  in  Teleosteans ;  these  are  the 
pterotic  and  sphenotic. 

(b)  Optic  capsule. 

The  eye  is  frequently  enclosed  in  a  cartilaginous  sclerotic 
capsule,  and  in  this  a  number  of  scale-like  bones  are  often 
developed. 

Several  membrane  bones  are  commonly  formed  around  the 
orbit  or  cavity  for  the  eye.  The  most  constant  of  these  is 
the  lachrymal  which  lies  in  the  anterior  corner;  frequently  too, 
as  in  Teleosteans,  there  is  a  supra-orbital  lying  in  the  upper 
part  of  the  orbit,  or  as  in  many  Reptiles,  a  postorbital  lying  in 
the  posterior  part  of  the  orbit. 

(c)  Nasal  capsule. 

In  relation  to  the  nasal  capsules  various  bones  occur. 


INTRODUCTORY.      JAWS    AND   VISCERAL   SKELETON.       21 

The  basicranial  axis  in  front  of  the  presphenoid  is  ossified,, 
as  the  mesethmoid,  dorsal  to  which  there  sometimes,  as  in 
Teleosteans,  occur  a  median  ethmoid  and  a  pair  of  lateral 
ethmoids1.  Two  pairs  of  membrane  bones  very  commonly 
occur  in  this  region,  viz.  the  nasals  which  lie  dorsal  to  the 
mesethmoid,  and  the  vomers  (sometimes  there  is  only  one)  which 
lie  ventral  to  it. 

The  part  of  the  skull  lying  immediately  in  front  of  the 
cranial  cavity  and  in  relation  to  the  nasal  capsules  constitutes 
the  ethmoidal  region. 

There  remain  certain  other  membrane  bones  which  are 
often  found  connected  with  the  cranium.  Of  these,  one  of 
the  largest  is  the  parasphenoid  which,  in  Ichthyopsids,  is 
found  underlying  the  basicranial  axis.  Prefrontals  often,  as 
in  most  reptiles,  occur  lying  partly  at  the  sides  and  partly  in 
front  of  the  frontal,  and  postfrontala  similarly  occur  behind  the 
orbit  lying  partly  behind  the  f rentals  and  partly  at  their  sides. 
Lastly  a  squamosal  bone  is,  as  in  Mammals,  very  commonly 
developed,  and  lies  external  and  partly  dorsal  to  the  auditory 
capsules. 

THE  JAWS  AND  VISCERAL  SKELETON. 

In  the  most  primitive  fish  these  consist  of  a  series  of 
cartilaginous  rings  or  arches  placed  one  behind  another  and 
encircling  the  anterior  end  of  the  alimentary  canal.  Originally 
they  are  mainly  concerned  with  branchial  respiration. 

The  first  or  maxillo-mandibular  arch  forms  the  upper 
jaw  and  the  lower  jaw  or  mandible. 

The  second  or  hyoid  arch  bears  gills  and  often  assists 
in  attaching  the  jaws  to  the  cranium.  The  remaining  arches 
may  bear  gills,  though  the  last  is  commonly  without  them. 

The  above  condition  is  only  found  in  fishes,  in  higher 
animals  the  visceral  skeleton  is  greatly  reduced  and  modified. 

The  first  or  maxillo-mandibular   arch   is  divisible  into  a 

1  Sometimes  also  called  ectethmoids  or  parethmoids. 


22  THE  VERTEBRATE  SKELETON. 

dorsal  portion,  the  palato-pterygo-quadrate  bar,  which 
forms  the  primitive  upper  jaw  and  enters  into  very  close 
relations  with  the  cranium,  and  a  ventral  portion,  Meckel's 
cartilage,  which  forms  the  primitive  lower  jaw.  The  carti- 
laginous rudiments  of  both  these  portions  disappear  to  a 
greater  or  less  extent  and  become  partly  ossified,  partly  re- 
placed by  or  enveloped  in  membrane  bone. 

The  posterior  part  of  the  palato-pterygo-quadrate  bar  be- 
comes ossified  to  form  the  quadrate,  the  anterior  part  to  form 
the  palatine  and  pterygoid,  or  the  two  latter  may  be  formed 
partially  or  entirely  of  periosteal  bone,  developed  round  the 
cartilaginous  bar.  Two  pairs  of  important  membrane  bones, 
the  premaxillae  and  maxillae  form  the  anterior  part  of  the 
upper  jaw,  and  behind  the  maxilla  lies  another  membrane 
bone,  the  jugal  or  malar,  which  is  connected  with  the  quadrate 
by  a  quadratojugal.  The  premaxillae  have  a  large  share  in 
bounding  the  external  nasal  openings  or  anterior  nares. 

In  lower  vertebrates  the  nasal  passage  leads  directly  into 
the  front  part  of  the  mouth  cavity  and  opens  by  the  posterior 
nares.  In  some  higher  vertebrates,  such  as  mammals  and 
crocodiles,  processes  arise  from  the  premaxillae  and  palatines, 
and  sometimes  from  the  pterygoids,  which  meet  their  fellows 
in  the  middle  line  and  form  the  palate,  shutting  off  the  nasal 
passage  from  the  mouth  cavity  and  causing  the  posterior  nares 
to  open  far  back. 

The  cartilage  of  the  lower  jaw  is  in  all  animals  with 
ossified  skeletons,  except  the  Mammalia,  partly  replaced  by 
cartilage  bone  forming  the  articular,  partly  overlain  by  a 
series  of  membrane  bones  the  dentary,  splenial,  angular, 
supra-angular  and  coronoid.  In  many  sharks  large  paired 
accessory  cartilages  occur  at  the  sides  of  the  jaws ;  and  in  a 
few  reptiles  and  some  Amphibia,  such  as  the  Frog,  the  ossified 
representative  of  the  anterior  of  these  structures  occurs 
forming  the  mento-meckelian  bone.  In  mammals  the  lower 
jaw  includes  but  a  single  bone. 


INTRODUCTORY.      RIBS   AND   STERNUM.  23 

The  quadrate  in  all  animals  with  ossified  skeletons,  except 
the  Mammalia,  forms  the  suspensorium  of  the  mandible  or  the 
skeletal  link  between  the  jaw  and  the  cranium ;  in  the  Mam- 
malia, however,  the  mandible  articulates  with  the  squamosal, 
while  the  quadrate  is  greatly  reduced,  and  is  now  generally 
considered  to  be  represented  by  the  tympanic  ring  of  the  ear. 

The  second  visceral  or  hyoid  arch  in  fishes  consists  of  two 
pieces  of  cartilage,  a  proximal1  piece  the  hyomandibular, 
and  a  distal1  piece  the  cerato-hyal.  The  cerato-hyals  of  the 
two  sides  are  commonly  united  by  a  median  ventral  plate,  the 
basi-hyal.  The  hyoid  arch  bears  gills  on  its  posterior  border, 
but  its  most  important  function  in  most  fishes  is  to  act  as  the 
suspensorium.  In  higher  vertebrates  the  representative  of 
the  hyomandibular  is  much  reduced  in  size,  and  comes  into 
relation  with  the  ear  forming  the  auditory  ossicles;  the 
cerato-hyal  looses  its  attachment  to  the  hyomandibular  and 
becomes  directly  attached  to  the  cranium,  forming  a  large  part 
of  the  hyoid  apparatus  of  most  higher  vertebrates. 

Behind  the  hyoid  arch  come  the  branchial  arches.  They 
are  best  developed  in  fishes,  in  which  they  are  commonly  five 
in  number  and  bear  gills.  Their  ventral  ends  are  united  in 
pairs  by  median  pieces,  the  copulae. 

In  higher  vertebrates  they  become  greatly  reduced,  and 
all  except  the  first  and  second  completely  disappear.  In  the 
highest  vertebrates,  the  mammals,  the  second  has  disappeared, 
but  in  birds  and  many  reptiles  it  is  comparatively  well 
developed. 

3.     THE  RIBS  AND  STERNUM. 

The  ribs  are  a  series  of  segmentally  arranged  cartilagi- 
nous or  bony  rods,  attached  to  the  vertebrae;  they  tend 
to  surround  the  body  cavity,  and  to  protect  the  organs 
contained  within  it.  Ribs  are  very  frequently  found 

1  The  proximal  end  of  anything  is  the  one  nearest  the  point  of  origin 
or  attachment,  the  distal  end  is  the  one  furthest  from  the  point  of  origin 
or  attachment. 


24  THE  VERTEBRATE  SKELETON. 

attached  to  the  transverse  processes  of  the  vertebrae,  but  a 
study  of  their  origin  in  fish  shows  that  they  are  really  the 
cut  off  terminations  of  the  ventral  arch,  not  of  the  transverse 
processes  which  are  outgrowths  from  the  dorsal  arch.  In  the 
tail  their  function  is  to  surround  and  protect  structures  like 
the  ventral  blood-vessels  which  do  not  vary  much  in  size, 
consequently  they  meet  one  another,  and  form  a  series  of 
complete  ventral  or  haemal  arches.  But  the  trunk  contains 
organs  like  the  lungs  and  stomach  which  are  liable  to  vary 
much  in  size  at  different  times,  consequently  the  halves  of  the 
haemal  arch  do  not  meet  ventrally,  and  then  the  ribs  become 
detached  from  the  rest  of  the  haemal  arch.  Having  once 
become  detached,  they  are  able  to  shift  about  and  unite  them- 
selves to  various  points  of  the  vertebra.  They  frequently,  as 
has  been  already  mentioned,  become  entirely  attached  to  the 
transverse  process,  or  they  may  be  attached  to  the  transverse 
process  by  a  dorsal  or  tubercular  portion  and  to  the  centrum 
or  to  the  ventral  arch  by  a  ventral  or  capitular  portion. 

In  all  animals  above  fishes  the  distal  ends  of  the  thoracic 
ribs  unite  with  a  median  breast  bone  or  sternum  which 
generally  has  the  form  of  a  segmented  rod.  The  sternum  is 
really  formed  by  the  fusion  of  the  distal  ends  of  a  series  of 
ribs.  In  many  animals  elements  of  the  shoulder  girdle  enter 
into  close  relation  with  the  rib  elements  of  the  sternum. 

II.     THE  APPENDICULAK  SKELETON. 

This  consists  of  the  skeleton  of  the  anterior  or  pectoral, 
and  the  posterior  or  pelvic  limbs,  and  their  girdles.  In  every 
case  (except  in  Chelonia)  the  parts  of  the  appendicular  skele- 
ton lie  external  to  the  ribs. 

1.     THE  LIMB  GIRDLES. 

The  Pectoral  girdle1.  In  the  simplest  case  the  pectoral 
or  shoulder  girdle  consists  of  a  hoop  of  cartilage  incomplete 

1  W.  K.  Parker,  A  Monograph  of  the  Shoulder  Girdle  and  Sternum, 
Ray  Soc.  London,  1868. 


INTRODUCTORY.      LIMB   GIRDLES.  25 

dorsally.  It  is  attached  by  muscle  to  the  vertebral  column, 
and  is  divided  on  either  side  into  dorsal  and  ventral  portions 
by  a  cavity,  the  glenoid  cavity,  at  the  point  where  the 
anterior  limb  articulates.  In  higher  fishes  this  hoop  is  dis- 
tinctly divided  into  right  and  left  halves  ;  it  becomes  more  or 
less  ossified,  and  a  pair  of  important  bones,  the  clavicles,  are 
developed  in  connection  with  its  ventral  portion. 

In  higher  vertebrates  ossification  sets  up  in  the  cartilage 
and  gives  rise  on  each  side  to  a  dorsal  bone,  the  scapula, 
and  frequently  to  an  anterior  ventral  bone,  the  precoracoid, 
and  a  posterior  ventral  bone,  the  coracoid.  The  precoracoid 
is  often  not  ossified,  and  upon  it  is  developed  the  clavicle 
which  more  or  less  replaces  it.  In  some  forms  a  T  shaped 
interclavicle  occurs,  in  others  epicoracoids  are  found  in  front 
of  the  coracoids.  In  all  vertebrata  above  fish,  except  the  great 
majority  of  mammals,  the  coracoids  are  large  and  articulate 
with  the  sternum.  But  in  mammals  the  coracoids  are  nearly 
always  quite  vestigial,  and  the  pectoral  girdle  is  attached  to 
the  axial  skeleton  by  the  clavicle  or  sometimes  by  muscles  and 
ligaments  only. 

The  Pelvic  girdle1  like  the  pectoral  consists  primitively 
of  a  simple  rod  or  hoop  of  cartilage,  which  in  vertebrata  above 
fishes  is  divided  into  dorsal  and  ventral  portions,  by  a  cavity, 
the  acetabulum,  with  which  the  posterior  limb  articulates. 
In  the  pelvic  girdle  as  in  the  pectoral  one  dorsal,  and  (com- 
monly) two  ventral  ossifications  take  place.  The  dorsal  bone 
is  the  ilium  and  corresponds  to  the  scapula.  The  posterior 
ventral  bone  is  the  ischium  corresponding  to  the  coracoid. 
The  anterior  ventral  bone  is  the  pubis  and  is  generally  com- 
pared to  the  precoracoid,  but  in  some  cases  a  fourth  pelvic 
element,  the  acetabular  or  cotyloid  bone  is  found,  and  this 
may  correspond  to  the  precoracoid. 

The  pelvic  girdle  differs  from  the  pectoral  in  the  fact  that 
the  dorsal  bones — the  ilia — are  nearly  always  firmly  united  to 
1  See  E.  Wiedersheim,  Zeitschr.  wiss.  Zool.  vol.  LIII.  suppl.  p.  43,  1892. 


26  THE  VERTEBRATE  SKELETON. 

transverse  processes  of  the  sacral  vertebrae,  by  means  of 
rudimentary  ribs.  The  pubes  and  ischia  generally  meet  in 
ventral  symphyses. 

2.     THE  LIMBS. 

It  will  be  most  convenient  to  defer  a  discussion  of  the 
limbs  of  fishes  to  chap.  vm. 

All  vertebrates  above  fishes  have  the  limbs  divisible  into 
three  main  segments  : — 

Anterior  or  Fore  limb.  Posterior  or  Hind  limb. 
Proximal  segment.      upper  arm  or  brachium.  thigh. 

Middle  segment.        fore-arm  or  antibrachium.  shin  or  cms. 

Distal  segment.  manus.  pes. 

The  proximal  segments  each  contain  one  bone,  the  hume- 
rus  in  the  case  of  the  upper  arm,  and  the  femur  in  the  case 
of  the  thigh.  The  middle  segments  each  contain  two  bones, 
the  radius  and  ulna  in  the  case  of  the  fore-arm,  and  the  tibia 
and  fibula  in  the  case  of  the  shin. 

The  manus  and  pes  are  further  subdivided  into 

(a)  two  or  three  proximal  rows  of  bones  forming  the 
wrist  or  carpus  in  the  case  of  the  manus,  and  the  ankle  or 
tarsus  in  the  case  of  the  pes. 

(b)  a  middle  row  called  respectively  the  metacarpus 
and  metatarsus. 

(c)  a   number  of   distal   bones  called  the  phalanges 
which  form  the  skeleton  of  the  fingers  and  toes,  or  digits. 

Typically  the  manus  and  pes  both  have  five  digits  (pente- 
dactylate).  The  first  digit  of  the  manus  is  commonly  called 
the  pollex,  and  the  first  digit  of  the  pes  the  hallux. 

In  a  very  simple  carpus  such  as  that  of  Chelydra,  there 
are  nine  bones.  They  are  arranged  in  a  proximal  row  of 


INTRODUCTORY.      THE   LIMBS.  27 

three,  the  radiale,  intermedium,  and  ulnare, — the  first  being 
on  the  radial  side  of  the  limb,  and  a  distal  row  of  five  called 
respectively  carpale  1,  2,  3,  4,  5,  beginning  on  the  radial  side. 
Between  these  two  rows  is  a  single  bone  the  centrale,  or  there 
may  be  two. 

Similarly  there  are  nine  bones  in  a  simple  tarsus  such  as 
that  of  Salamandra.  They  form  a  proximal  row  of  three,  the 
tibiale,  intermedium  and  fibulare,  and  a  distal  row  of  five, 
called  respectively  tarsale  1,  2,  3,  4,  5,  beginning  on  the  tibial 
side.  Between  the  two  rows  there  is  a  centrale  as  in  the 
carpus,  or  there  may  be  two. 

The  following  names  derived  from  human  anatomy  are 
commonly  applied  to  the  various  carpal  and  tarsal  bones  : 

Carpus.  Tarsus. 

radiale  =  scaphoid  tibiale  ) 

,.  ,.       V  astragalus 

intermedium  =  lunar  intermedium] 

ulnare  =  cuneiform  fibulare  =  calcaneum 

centrale  =  central  centrale  =  navicular 

carpale  1  =  trapezium  tarsale  1  =  internal  cuneiform 
,,       2  =  trapezoid  ,,      2  =  middle         ,, 

,,       3  =  magnum  ,,      3  =  external       ,, 


"         I  Cuneiform  "      rl  = 

„       5j  ,,      5J 


cuboid 


NOTE.  The  above  is  the  view  commonly  accepted  concerning  the 
homology  of  the  carpal  and  tarsal  bones.  But  with  regard  to  the 
proximal  row  of  tarsal  bones  there  is  difference  of  opinion.  All  anato- 
mists are  agreed  that  the  calcaneum  is  the  fibulare  and  that  the  inter- 
medium is  contained  in  the  astragalus,  but  while  the  majority  regard 
the  astragalus  as  the  fused  tibiale  and  intermedium,  Baur  considers 
that  a  small  bone  found  on  the  tibial  side  of  the  tarsus  in  Procavia, 
many  Eodents,  Insectivores,  and  the  male  Ornithorhynchus,  is  the  vesti- 
gial tibiale,  and  regards  the  astragalus  as  the  intermedium  alone1.  He 
also  considers  that  the  mammalian  scaphoid  represents  a  centrale. 

1  G.  Baur,  Beitrdge  zur  Morphogenie  des  Carpus  und  Tarsus  der 
Vertebraten,  Theil  1.  Batrachia.  Jena,  1888,  and  Amer.  Natural.,  vol.  xix. 
1885  (several  papers). 


28  THE  VERTEBRATE  SKELETON. 

MODIFICATIONS  IN  THE  POSITIONS  OF  THE  LIMBS'. 

In  their  primitive  position  the  limbs  are  straight  and  are 
extended  parallel  to  one  another  at  right  angles  to  the  axis  of 
the  trunk.  Each  limb  then  has  a  dorsal  surface,  a  ventral 
surface,  an  anterior  or  pre- axial  edge,  and  a  posterior  or 
postaxial  edge. 

In  the  anterior  limb  the  radius  and  the  pollex  are  pre- 
axial,  the  ulna  and  the  fifth  finger  are  postaxial.  In  the 
posterior  limb  the  tibia  and  the  hallux  are  pre-axial,  the  fibula 
and  the  fifth  toe  are  postaxial.  The  Cetacea  and  various  extinct 
reptiles,  such  as  Ichthyosaurus  and  Plesiosaurus,  have  their 
limbs  in  practically  this  primitive  position. 

The  first  modification  from  it  is  produced  by  the  bending 
ventrally  of  the  middle  segments  of  both  limbs  upon  the 
proximal  segments,  while  the  distal  segment  is  bent  in  the 
opposite  direction  on  the  middle  segment.  Then  the  ventral 
surfaces  of  the  antibrachium  and  crus  come  to  look  inwards, 
and  their  dorsal  surfaces  to  look  outwards.  The  brachium 
and  manus,  thigh  and  pes  still  have  their  dorsal  surfaces 
facing  upwards  and  their  ventral  surfaces  facing  downwards 
as  before,  and  the  relations  of  their  pre-  and  postaxial  borders 
remain  as  they  were.  Many  Amphibians  and  Reptiles,  such 
as  tortoises,  carry  their  limbs  in  this  position. 

In  all  higher  vertebrates,  however,  a  further  change  takes 
place,  each  limb  is  rotated  as  a  whole  from  its  proximal  end, 
the  rotation  taking  place  in  opposite  directions  in  the  fore  and 
hind  limbs  respectively.  The  anterior  limb  is  rotated  back- 
wards from  the  shoulder,  so  that  the  brachium  lies  nearly  parallel 
to  the  body,  and  the  elbow  points  backwards,  the  antibrachium 
downwards,  and  the  manus  backwards  ;  the  pre-axial  surface  of 
the  whole  limb  with  the  radius  and  pollex  now  faces  outwards, 
and  the  postaxial  surface  with  the  ulna  and  fifth  finger  now  faces 

1  This  account  is  based  on  Chapter  XX.  of  Flower's  Osteology  of  the 
Mammalia.  London  1876. 


INTRODUCTORY.      POSITIONS   OF   THE   LIMBS.  29 

inwards.  In  the  Walrus  and,  to  a  certain  extent,  in  the  Sea- 
lions  the  anterior  limb  remains  throughout  life  in  this  position. 
The  posterior  limb  is  also  rotated,  but  the  rotation  in  this 
case  takes  place  forwards,  so  that  the  thigh  lies  nearly  parallel 
to  the  body,  the  knee-joint  pointing  forwards ;  the  crus  down- 
wards and  the  pes  forwards.  The  pre-axial  surface  of  the 
whole  limb  with  the  tibia  and  hallux  looks  towards  the  middle 
of  the  body,  the  postaxial  surface  with  the  fibula  and  fifth  toe 
looks  outwards.  This  is  the  position  in  which  the  hind  limb 
is  carried  in  nearly  all  mammals. 

In  nearly  all  mammals  a  further  change  takes  place  in  the 
position  of  the  anterior  limb.  The  radius  and  ulna  have 
hitherto  been  parallel  to  one  another,  but  now  the  lower  end 
of  the  radius,  carrying  with  it  the  manus,  comes  to  be  rotated 
forwards  round  the  ulna,  so  that  the  manus,  as  well  as  the 
pes,  comes  to  be  forwardly-directed,  and  its  pre-axial  surface 
faces  inwards. 

In  the  majority  of  mammals  the  radius  and  ulna  are  per- 
manently fixed  in  this,  which  is  known  as  the  prone  position, 
but  in  man  and  some  other  mammals  the  manus  can  be 
pronated  or  turned  into  this  position  at  will.  When  the 
radius  and  ulna  are  parallel  throughout  their  whole  length 
the  manus  is  said  to  be  in  the  supine  position. 

The  extensor  side  of  a  limb  is  that  to  which  the  muscles 
which  straighten  it  are  attached,  the  flexor  side  is  that  to 
which  the  muscles  which  bend  it  are  attached. 


CHAPTER  II. 
CLASSIFICATION. 

THE  following  classification  includes  only  the  forms 
mentioned  in  the  succeeding  pages.  The  relative  value  of 
some  of  the  terms  employed  in  classification  is  not  identical 
throughout  the  book.  This  remark  applies  specially  to  the 
term  group,  which  is  a  convenient  one,  owing  to  its  not  having 
such  a  hard  and  fast  zoological  meaning  as  has  the  term  family, 
for  instance.  The  term  group  is  applied  in  this  book  to 
divisions  of  the  animal  kingdom  of  very  different  classificatory 
importance. 

PHYLUM  CHORDATA. 

SUBPHYLUM  A.     HEMICHORDATA. 

Balanoglossus. 
Cephalodiscus. 
Rhabdopleura. 
1  Phoronis. 

(?  Actinotrocha — larval  Phoronis). 

% 

SUBPHYLUM  B.     UROCHORDATA  (TUNICATA). 
Group  LARVACEA  and  others. 

SUBPHYLUM  C.     CEPHALOCHORDATA. 

Amphioxus — laricelet. 

NOTE.     In  this  chapter  all  the  generic  names  printed  in  italics  are 
those  of  extinct  animals. 


CLASSIFICATION.  31 

SUBPHYLUM  D.     VERTEBRATA. 
DIVISION  (I).     CYCLOSTOMATA. 

Order  1.     MARSIPOBRANCHII. 
Family  Myxinoidei.     Myxine — hag-fish. 

Bdellostoma. 
Family  Petromyzontidae.     Petromyzon — lamprey. 

(Ammocoetes — larval  lamprey.) 
Family  Palaeospondylidae.     Palaeospondylus. 

Order  2.     OSTRACODERMI. 
Suborder  1.     HETEROSTRACI. 
Family  Pteraspidae.     Pteraspis. 

Suborder  2.     OSTEOSTRACI. 
Family  Cephalaspidae.     Cephalaspis. 

Suborder  3.     ANTIARCHA. 
Family  Asterolepidae.     Pterichttiys. 
Asterolepis. 

DIVISION  (II).     GNATHOSTOMATA. 
A.     ICHTHYOPSIDA. 

CLASS  I.     PISCES. 
Order  1.     ELASMOBRANCHII. 
Suborder  (1).     ICHTHYOTOMI. 
Family  Pleuracanthidae.     Xenacanthus. 
Suborder  (2).     PLEUROPTERYGII. 

Cladoselache. 
Suborder  (3).     SELACHII. 

Group  SQUALIDAE. 

Family  Notidanidae.     Heptanchus. 
Hexanchus. 

Chlamydoselache — frill-gilled  shark. 
Family  Cochliodontidae.     Cochliodus. 


32  THE  VERTEBRATE  SKELETON. 

Family     Cestraciontidae.      Cestracion — Port     Jackson 

shark. 
Acrodus, 

Family  Scylliidae.     Scyllium — spotted  dog-fish. 
Family  Lamnidae.     Odontaspis. 
Family  Carcharidae.     Galeus — tope. 
Family  Spinacidae.     Acanthias — spiny  dog-fish. 

Scymnus. 
Family  Squatinidae.     Squatina  (Rhina) — angel  fish. 

Group  BATOIDEI. 

Family  Pristidae.     Pristis — saw-fish. 
Family  Raiidae.     Raia— skate. 
Family  Myliobatidae.     Myliobatis — eagle  ray. 
Family  Trygonidae.     Trygon — sting  ray. 
Family  Torpedinidae.     Torpedo — electric  ray. 

Suborder  (4).     ACANTHODII. 
Family  Acanthodidae.      Acanthodes. 
Family  Diplacanthidae.     Diplacanthus. 

Order  2.     HOLOCEPHALI. 

Family  Chimaeridae.     Chimaera — rabbit  fish. 
Harriotta. 
Callorhynchus. 
Ischyodus. 

Order  3.     GANOIDEI. 
Suborder  (1).     CHONDROSTEI. 
Family  Palaeoniscidae.     Palaeoniscus, 

Trissolepis. 
Family  Acipenseridae.     Acipenser — sturgeon. 

Scaphirhynchus. 

Family  Polyodontidae.     Polyodon    (Spatularia) — spoon- 
beaked  sturgeon. 
Psephurus — slender-beaked  sturgeon. 


CLASSIFICATION.  33 

Suborder  (2).     CROSSOPTERYGII. 
Family  Holoptychiidae.     Holoptychius. 
Family  Rhizodontidae.     Rhizodus. 
Family  Osteolepidae.     Osteolepis. 
Family  Polypteridae.     Polypterus — bichir. 

Calamoichthy  s — reed-fish . 

Suborder  (3).     HOLOSTEI. 

Family  Lepidosteidae.     Lepidosteus — gar  pike. 
Family  Semionotidae.     Lepidotus. 
Family  Amiidae.     Amia — bow-fin. 

Order  4.     TELEOSTEI. 

Suborder  (1).     PLECTOGNATHI. 
Family  Balistidae.     Balistes— file-fish. 
Family  Gymnodontidae.     Diodon — globe-fish. 
Family  Ostracionidae.     Ostracion — coffer-fish. 

Suborder  (2).     PHYSOSTOMI. 
Family  Siluridae — cat-fishes. 
Family  Cyprinidae.     Cyprinus — carp. 
Family  Esocidae.     Esox — pike. 
Family  Salmonidae.     Salmo — salmon. 
Family  Clupeidae.     Clupeus — herring. 

Exocaetus — 'flying  fish'. 
Family  Muraenidae.     Anguilla — eel. 

Suborder  (3).     ANACANTHINI. 

Family  Gadidae.     Gadus — cod,  haddock,  whiting. 
Family  Pleuronectidae.     Solea — sole. 

Suborder  (4).     PHARYNGOGNATHI. 
Family  Labridae.     Labrus — wrasse. 

Scarus — parrot  fish. 
R.  3 


34  THE   VERTEBRATE    SKELETON. 

Subordei    (5).     ACANTHOPTERYGII. 

Family  Cataphracti.     Dactylopterus — flying  gurnard. 
Family  Percidae.     Perca — perch. 

Order  5.     DIPNOI. 
Suborder  (1).     SIRENOIDEI. 
Family  Dipteridae.     .Dipterus. 

Family  Monopneumona.     Ceratodus — barramunda. 
Family  Dipneumona.     Protopterus — African  mud-fish. 

Lepidosiren. 

Suborder  (2).     ARTHRODIRA. 
Family  Coccosteidae.     Coccosteus. 
Dinichthys. 

NOTE.  Palaeontological  research  has  disclosed  the  existence  of  a  great 
number  of  forms  which  seem  to  connect  with  one  another  almost  all  the 
orders  of  fishes  as  usually  recognised.  Forms  connecting  the  living 
Ganoids  with  the  Teleosteans  have  been  especially  numerous,  so  that 
these  terms  Ganoid  and  Teleostean  can  hardly  be  any  longer  used  in  a 
precise  and  scientific  sense.  This  has  rendered  the  subject  of  the  classifi- 
cation of  fishes  a  very  difficult  one.  Though  unsuitable  for  adoption  in 
a  work  like  the  present,  by  far  the  most  natural  classification  hitherto 
proposed  seems  to  be  that  of  Smith  Woodward1.  He  considers  that  the 
course  of  development  of  fishes  has  followed  two  distinct  lines,  the  auto- 
stylic  and  hyostylic  (see  p.  119),  and  groups  the  various  forms  as  follows: 

HYOSTYLIC.  AUTOSTYLIC. 

Subclass  1.     ELASMOBKANCHII.  Subclass  3.     HOLOCEPHALI. 

1.  Ichthyotomi.  1.     (unknown). 

2.  Selachii.  2.     Chimaeroidei. 

3.  Acanthodii.  3.     (unknown). 
Subclass  2.     TELEOSTOMI.                       Subclass  4.     DIPNOI. 

1.  Crossopterygii      (Palaeozoic  1.     Sirenoidei. 

and  Mesozoic). 

2.  Crossopterygii  (Cainozoic).  2.     (unknown). 

3.  Actinopterygii.  3.     Arthrodira. 

The  primitive  forms  in  each  of  these  four  subclasses  have  the  fins 
archipterygia  (see  p.  127). 

1  A.  Smith  Woodward,  Catalogue  of  Fossil  Fishes  in  the  British 
Museum,  Part  II.,  Introduction,  p.  xii. 


CLASSIFICATION.  35 

CLASS  II.     AMPHIBIA. 

Order  1.     URODELA. 
Suborder  (1).     ICHTHYOIDEA. 
Group  A,     PERENNIBRANCHIATA. 
Family  Menobranchidae.     Menobranchus. 
Family  Proteidae.     Proteus— olm. 
Family  Sirenidae.     Siren. 

Group  B.     DEROTREMATA. 
Family  Amphiumidae.     Megalobatrachus. 

Cryptobranchus  (Menopoma). 
Amphiuma. 

Suborder  (2).     SALAMANDRINA. 

Family  Salamandridae.     Salamandra-  salamander. 

Molge — newt. 
Onychodactylus. 
Amblystoma. 

(Siredon — axolotl,   larval  Am- 
blystoma). 
Batrachoseps. 
Spelerpes  (Gyrinophilus). 

Order  2.     LABYRINTHODONTIA. 
Group  Lepospondyli.     Branchiosauru*. 
Group  Temnospondyli.     Archegosaurus. 

Nyrania. 
Euchirosaurus. 
Group  Stereospondyli.     Capitosaurus. 

Mastodonsaurus. 
Order  3.     GYMNOPHIONA. 
Family  Caeciliidae.     Siphonops. 
Epicrium. 

3—2 


36  THE   VERTEBRATE   SKELETON. 

Order  4.     ANURA. 
Suborder  (1).     AGLOSSA. 
Family  Xenopidae.     Xenopus. 
Family  Pipidae.     Pipa — Surinam  toad. 

Suborder  (2).     PHANEROGLOSSA. 

Group  ARCIFERA. 
Family  Discoglossidae.     Discoglossus — painted  frog. 

Bombinator — fire-bellied  frog. 
Alytes — midwife  frog. 

Family  Pelobatidae.     Pelobates — toad  frog. 
Family  Hylidae.     Hyla — green  tree-frog. 
Family  Bufonidae.     Bufo — toad. 

Docidophryne. 
Family  Cystignathidae.     Ceratophrys — horned  frog. 

Group    FlRMISTERNIA. 

Family  Ranidae.     Rana — common  and  edible  frogs. 
Family  Engystomatidae.     Brachycephalus. 

B.     SAUROPSIDA. 

CLASS  I.     REPTILIA1. 

Order  1.     THEROMORPHA. 

Group  Anomodontia.     Dicynodon. 

Udenodon. 

Group  Placodontia.     Placodus. 
Group  Pariasamia.     Pariasaurus. 

Elginia. 

Group  Theriodontia.     Dimetrodon. 
Galesaurus. 
Cynognathus. 

1  This  classification  of  reptiles  is  mainly  based  on  that  of  Lydekker 
(Catalogue  of  Fossil  Reptiles  in  the  British  Museum)  but  in  some  respects 
that  of  von  Zittel  has  been  followed. 


CLASSIFICATION.  37 

Order  2.     SAUROPTERYGIA. 
Family  Mesosauridae.     Mesosaurus. 
Family  Nothosauridae.     Nothosaurus. 
Family  Plesiosauridae.     Plesiosaurus. 

Pliosaurus. 

Order  3.     CHELONIA. 
Suborder  (1).     TRIONYCHIA. 
Family  Trionychidae.     Trionyx— snapping  turtle. 

Suborder  (2).     CRYPTODIRA. 
Family  Dermochelydidae.      Dermochelys    (Sphargis) — 

leathery  turtle. 

Family  Chelonidae.     Ohelone — green  turtle. 
Family  Chelydridae.     Chelydra — terrapin. 
Family  Chersidae.     Testudo — tortoise. 
Suborder  (3).     PLEURODIRA. 
Family  Chelydae.     Chelys. 

Order  4.     ICHTHYOSAURIA. 
Family  Ichthyosauridae.     Ichthyosauriis. 

Order  5.     RHYNCHOCEPHALIA. 
Suborder  (1).     RHYNCHOCEPHALIA  VERA. 
Family  Sphenodontidae.     Sphenodon  (Hatteria). 
Family  Rhynchosauridae.     Hyperodapedon. 

Suborder  (2).     PROGANOSAURIA. 
Family  Proterosauridae.     Proterosaurus. 

Order  6.     SQUAMATA. 

Suborder  (1).     LACERTILIA. 

Group  Lacertilia  vera. 
Family  Geckonidae.     Gecko. 
Family  Pygopodidae.     Lialis — scale-foot. 


38  THE    VERTEBRATE    SKELETON. 

Family  Agamidae.     Draco — flying  lizard. 

Agama. 

Family  Iguanidae.     Iguana. 
Family  Anguidae.     Ophisaurus  (Bipes,  Pseudopus). 

Anguis — blindworm. 

Family  Varanidae.     Yaranus — monitor. 
Family  Amphisbaenidae.     Chirotes. 

Amphisbaena. 

Family  Scincidae.     Tiliqua  (Cyclodus). 
Scincus — skink. 
Chalcides  (Seps). 

Group  Rhiptoglossa. 
Family  Chamaeleonidae.     Chamaeleon. 

Suborder  (2).     OPHIDIA. 

Family  Typhlopidae.     Typhlops — blind  snake. 
Family  Boidae.     Python. 

Family  Colubridae.     Tropidonotus — ringed  snake. 
Family  Hydrophidae — sea  snakes. 
Family  Crotalidae.     Crotalus — rattlesnake. 

Suborder  (3).     PYTHONOMORPHA. 
Family  Mosasauridae.     Mosasaurus. 

Order  7.     DINOSAURIA. 
Suborder  (1).     SAUROPODA. 
Family  Atlantosauridae.     Brontosaurus. 
Family  Cetiosauridae.     Morosaurus. 

Suborder  (2).  THEROPODA. 

Family  Megalosauridae.     Megalosaurus  (Ceratosaurus). 
Family  Compsognathidae.     Compsognathus. 


CLASSIFICATION.  39 

Suborder  (3).    ORTHOPODA. 

Section  (a).  STEGOSAURIA. 
Family  Scelidosauridae.  Polacanthus. 
Family  Stegosauridae.  Stegosaurus. 

Section  (b).     CERATOPSIA. 
Family  Ceratopsidae.     Polyonax  (Ceratops). 

Section  (c).     ORNITHOPODA. 
Family  Camptosauridae.     Hypsilophodon. 
Family  Iguanodontidae.     Iguanodon. 
Family  Hadrosauridae.     Hadrosaurus. 

Order  8.     CROCODILIA. 
Suborder  (1).     PARASUCHIA. 
Family  Phytosauridae.     Phytosaurus  (Belodon). 

Suborder  (2).     EUSUCHIA. 

Family  Teleosauridae.     Teleosaurus. 

Metriorhynchus. 

Family  Goniopholidae.     Goniopholis. 
Family  Alligatoridae.     Alligator. 

Caiman. 

Jacare. 

Family  Crocodilidae.     Crocodilus. 
Family  Garialidae.     Garialis  (Gavialis). 

Order  9.     PTEROSAURIA. 

Family  Pterodactylidae.     Pterodactylus. 

Family  Rhamphorhynchidae.     Rhamphorhynchus. 

Family  Pteranodontidae.     Pteranodon. 


40  THE    VERTEBRATE   SKELETON. 

CLASS  II.     AYES1. 

Subclass  (I).     ARCHAEORNITHES. 
Archaeopteryx. 

Subclass  (II).     NEORNTTHES. 

Order  1.     RATITAE. 
Group  .flSpyornithes. 


Group  Apteryges.     Apteryx  —  kiwi. 

Group  Dinornithes.     Moas. 

Group  Megistanes.     Casuarius  —  cassowary. 

Dromaeus  —  emeu. 

Group  Rheornithes.     Rhea  —  American  ostrich, 
Group  Struthiornithes.     Struthio  —  ostrich. 

Order  2.     ODONTOLCAE. 
wrornis. 


Order  3.     CARINATAE. 

Group  Iehthyomithiforrn.es. 

I chiliy  or  nis. 

Apatornis. 

Odontopteryx. 

Group  Colymbiformes. 
Subgroup  Colymbi — divers. 

Group  Sphenisciform.es. 

Subgroup  Sphenisci — penguins. 

1  This  classification  of  birds  is  essentially  that  of  Gadow  and  Selenka 
in  Bronn's  Classen  und  Ordnungen  des  Thier-reichs,  Band  vi.,  Abth.  iv., 
Vogel.  Leipzig,  1891. 


CLASSIFICATION.  41 

Group  Ciconiiformes. 

Subgroup  Steganopodes.     Sula — gannet. 

Pelicanus — pelican. 
Phaethon — frigate  bird. 
Phalacrocorax — cormorant. 
Subgroup  Ardeae.       Ardea — heron 
Subgroup  Ciconiae.     Leptoptilus — adjutant. 
Ciconia — white  stork. 

Group  Anseriformes. 

Subgroup  Palamedeae.     Palamedea) 

f  screamers. 
Chauna      J 

Subgroup  Anseres.     Anas — wild  duck. 
Anser — goose. 

Plectropterus — spur-winged   goose. 
Cygnus — swan. 
Mergus — merganser. 

Group  Falconiformes. 

Subgroup  Cathartae.     Cathartes — American  vulture. 
Subgroup  Accipitres.     Falco — falcon. 

Vultur — vulture. 

Harpagus. 

Gypogeranus — secretary  bird. 

Group  Tinamiform.es. 

Subgroup  Tinami.     Tinamus. 

Group  Galliform.es. 

Subgroup  Galli.     Gallus — fowl. 

Pavo — peacock. 
Subgroup  Opisthocomi.     Opisthocomus — hoatzin. 

Group  Gruiformes. 

Gruidae — cranes. 

Group  Stereornithes.     Phororhacos. 


42  THE  VERTEBRATE  SKELETON. 

Group  Charadriiformes. 

Subgroup  Limicolae.     Charadriidae — plovers. 

Parra — jacana. 

Subgroup  Lari.      Laridae — gulls. 
Alcidae — auks. 

Subgroup  Pteroclidae.     Pterocles — sandgrouse. 
Subgroup  Columbidae.     Columbae — pigeons. 
Didus — dodo. 
Pezophaps — solitaire. 
Group  Cueuliformes. 

Subgroup  Cuculi.     Scythrops. 

Subgroup  Psittaci.     Stringops — owl-parrot. 

Group  Coraeiiformes. 

Subgroup  Coraciae.     Coracias — roller. 

Buceros — hornbill. 
Upupa — hoopoe. 
Subgroup  Striges.     Owls. 
Subgroup  Cypseli.     Cypselidae — swifts. 

Trochilidae — humming-birds. 
Subgroup  Trogonidae.     Trogons. 
Subgroup  Pici.     Rhamphastos — toucan. 
Picus — woodpecker. 

Group  Passeriformes.     Crows,    finches,   larks,  warblers, 

and  many  others. 

C.     MAMMALIA1. 
Class  MAMMALIA. 

Subclass  (I).     ORNITHODELPHIA  or  PROTOTHERIA. 
Order.     MOJJOTREMATA. 

1  The  classification  adopted  is  almost  entirely  that  given  in  Flower 
and  Lydekker's  Mammals  Living  and  Extinct.     London,  1891. 


CLASSIFICATION.  43 

Family     Ornithorhynchidae.     Ornithorhynchus duck- 
bill. 

Family  Echidnidae.     Echidna — spiny  anteater. 
Group  Multituberculata.     Tritylodon. 

Subclass  (II).     DIDELPHIA  or  METATHERIA. 

Order.     MARSUPIALIA. 
Suborder  (1).     POLYPROTODONTIA. 
Family  Amphitheriidae.     Phascolotherium. 

Family  Didelphyidae.     Didelphys opossum. 

Family  Dasyuridae.     Thylacinus— Tasmanian  wolf. 
Sarcophilus — Tasmanian  devil. 
Dasyurus. 
Family  Peramelidae.     Perameles—  bandicoot. 

Choeropus. 
Family  Notoryctidae.     Notoryctes— marsupial  mole. 

Suborder   (2).     DIPROTODONTIA. 

Family  Phascolomyidae.     Phascolomys— wombat. 
Family  Phalangeridae.     Tarsipes. 

Phalanger — cuscus. 
Phascolarctus — koala. 
Tkylacoleo. 

Family  Diprotodontidae,     Diprotodon. 
Family  Nototheriidae.     Nototherium. 
Family   Macropodidae.     Macropus—  kangaroo. 
Family  Epanorthidae.     Coenolestes. 

Subclass   (III).     MONODELPHIA  or  EUTHERIA. 
Order  1.     EDENTATA. 

Family  Bradypodidae.     Bradypus  ) 

nu  1  r — sloths. 

CholoepusJ 


44  THE   VERTEBRATE   SKELETON. 

Family  Megatheriidae.     Megatherium— ground  sloth. 
Family  Myrmecophagidae.    Myrmecophaga — great  ant- 
eater. 

Cycloturus — two-toed    ant- 
eater. 

Family  Dasypodidae.     ChlamydophorusA 
Dasypus 
Priodon  -armadillos. 

Tatusia 

Family  Glyptodontidae.  Glyptodon. 
Family  Manidae.  Manis — pangolin. 
Family  Orycteropodidae.  Orycteropus — aard  vark. 

Order   2.     SIREXIA. 

Family  Manatidae.     Manatus — manatee. 
Family  Rhytinidae.     Rhytina — S  teller's  sea-cow. 
Family  Halicoridae.     Halicore — dugong. 
Family  Halitheriidae.     Halitherium. 

Order  3.     CETACEA. 
Suborder  (1).     ARCHAEOCETI. 
Family  Zeuglodontidae.     Zeuglodon. 

Suborder  (2).     MYSTACOCETI  or  BALAENOIDEA. 
Family  Balaenidae.     Balaena— right  whale. 

Megaptera — humpbacked  whale. 
Balaenoptera — rorqual. 

Suborder  (3).     ODONTOCETI. 
Family  Physeteridae.     Physeter— sperm  whale. 

Hyperoodon — bottlenose. 

Ziphius. 

Mesoplodon. 
Family  Physodontidae.     Physodon. 


CLASSIFICATION.  45 

Family  Squalodontidae.     Squalodon. 
Family  Platanistidae.     Platanista— Gangetic  dolphin. 
Inia. 

Pontoporia. 
Family  Delphinidae.     Monodon — narwhal. 

Phocaena — porpoise. 

Orca — killer. 

Globicephalus — Ca'ing  whale. 

Grampus. 

Lagenorhynchus. 

Delphinus — dolphin. 

Tursiops. 

Prodelphinus. 

Order  4.     UNGULATA. 
Division  A.     UNGULATA  VERA. 
Suborder  (1).     ARTIODACTYLA. 

Section  (a).     SUINA. 

Family  Hippopotamidae.     Hippopotamus. 
Family  Suidae.     Sus — pig. 
Babirussa. 

Phacochaerus — wart  hog. 
Hyotherium. 
Family  Cotylopidae.     Cotylops  (Oreodon). 

Cyclopidius. 

Family  Agriochoeridae.     Agriochoerus. 
Family  Anoplotheriidae.     Anoplotherium. 

Section  (b).     TFLOPODA. 
Family  Camelidae.     Camelus— camel. 

A  uchenia — llama. 
Section  (c).     TRAGULINA. 

Family  Tragulidae.     Dorcatherium  (Hyomoschus)— 
chevrotain. 


46  THE  VERTEBRATE  SKELETON. 

Section  (d).     RUMINANTIA  or  PECORA. 

Family  Cervidae.     Moschus — musk  deer. 
Cervus — deer. 
Cervulus — muntjac. 
Hydropotes — Chinese  water  deer. 
Family  Giraffidae.     Giraffa — giraffe. 

iSivatherium. 

Family  Antilocapridae.     Antilocapra — prongbuck. 
Family  Bovidae.     Tetraceros — four-horned  antelope. 
Gazella — gazelle. 
Bos — ox. 
Bison. 
Bubalus — buffalo. 

Suborder  (2).     PERISSODACTYLA. 
Family  Tapiridae.     Tapirus — tapir. 
Family  Lophiodontidae.     Lophiodon. 

Hyracotherium. 

Family  Palaeotheriidae.     Palaeotherium. 
Family  Equidae.     Hipparion. 

Equus — horse. 
Family  Rhinoeerotidae.     Rhinoceros. 

Elasmotherium. 
Family  Titanotheriidae.     Titanotherium  (Brontops). 

Palaeosyops. 

Family  Chalicotheriidae.     Chalicotherium. 
Family  Macraucheniidae.     Macrauchenia. 

Division  B.     SUBUNGULATA. 

Suborder  (1).     TOXODONTIA. 
Family  Astrapotheriidae.     Astrapotherium. 
Family  Nesodontidae.     Nesodon. 
Family  Toxodontidae.     Toxodon. 
Family  Typotheriidae.     Typotkerium. 


CLASSIFICATION.  47 

Suborder  (2).     CONDYLARTHRA. 
Family  Phenacodontidae.     Phenacodus. 

Suborder  (3).     HYRACOIDEA. 
Family  Hyracidae.     Procavia  (Hyrax). 

Suborder  (4).     AMBLYPODA. 
Family  Coryphodontidae.     Coryphodon. 
Family  Uintatheriidae.     Uintatherium  (Dinoceras). 

Suborder  (5).     PROBOSCIDEA. 
Family  Dinotheriidae.     Dinotlierium. 
Family  Elephantidae.     Mastodon. 

Elephas — elephant. 

Group    TlLLODONTIA. 

Order  5.     RODENTIA. 
Suborder  (1).     SIMPLICIDENTATA. 

Section  SCIUROMORPHA. 
Family  Castoridae.     Castor — beaver. 

Section  MYOMORPHA. 
Family  Lophiomyidae.     Lophiomys. 
Family  Muridae.     Hydromys. 

Acanthomys — spiny  mouse. 
Mus — mouse. 

Family  Spalacidae.     Bathyergus. 
Family  Dipodidae.     Dipus — jerboa. 

Pedetes — Cape  jumping-hare. 

Section  HYSTRTCOMORPHA. 
Family  Hystricidae.     Hystrix— porcupine. 
Family  Chinchillidae.     Chinchilla. 

Lagostomus — viscacha. 


48  THE   VERTEBRATE   SKELETON. 

Family  Dasyproctidae.     Coelogenys — paca. 

Dasyprocta — agouti. 

Family  Caviidae.     Cavia — guinea-pig. 

Hydrochaer  us — capybara . 

Suborder  (2).     DUPLICIDENTATA. 
Family  Leporidae.     Lepus — hare  and  rabbit. 

Order  6.     CARNIVORA. 
Suborder  (1).     CREODONTA. 
Family  Hyaenodontidae.     Hyaenodon. 

Suborder  (2).     CARNIVORA  VERA  or  FISSIPEDIA. 
Section  ^LUROIDEA. 

Family  Felidae.     Felis — cat,  lion,  tiger. 

Machaerodus — sabre-toothed  lion. 

Family  Viverridae.     Viverra — civet. 

Paradoxurus — palm  civet. 

Family  Protelidae.      Pro  teles — aard  wolf. 
Family  Hyaenidae.    Hyaena. 

Section.     CYNOIDEA. 
Family  Canidae.     Canis— dog,  wolf,  fox. 

Section  ARCTOIDEA. 
Family  Ursidae.     Ursus — bear. 
Family  Mustelidae.     Latax — sea  otter. 

Suborder  (3).     PINNIPEDIA. 
Family  Otariidae.     Otaria — sea  lion. 
Family  Trichechidae.     Trichechus — walrus. 
Family  Phocidae.     Ogmorhinus — sea  leopard. 

Order  7.     INSECTIVORA. 
Suborder  (1).     DERMOPTERA. 
Family  Galeopithecidae.  Galeopithecus — 'flying  lemur'. 


CLASSIFICATION.  49 

Suborder  (2).     INSECTIVORA  VERA. 

Family  Macroscelidae.     Macroscelides— jumping  shrew. 
Family  Erinaceidae.     Erinaceus — hedgehog. 

Gymnura. 

Family  Soricidae.     Sorex — shrew. 
Family  Talpidae.     Talpa — mole. 
Family  Potamogalidae.     Potamogale. 
Family  Solenodontidae.     Solenodon. 
Family  Centetidae.     Microgale. 

Centetes — tenrec. 
Family  Chrysochloridae.     Chrysochloris— golden  mole. 

Order  8.     CHIROPTERA. 

Suborder  (1).  MEGACHIROPTERA. 
Family  Pteropidae.  Pteropus — flying  fox. 

Suborder  (2).  MICROCHIROPTERA. 
Family  Rhinolophidae.  Horse-shoe  bats. 
Family  Phyllostomatidae.  Desmodus — vampire. 

Order  9.     PRIMATES. 
Suborder  (1).     LEMUROIDEA. 
Family  Tarsiidae.     Tarsius — tarsier. 
Family  Chiromyidae.     Chiromys— aye  aye. 

Suborder  (2).  ANTHROPOIDEA. 
Family  Hapalidae.  Hapale — marmoset. 
Family  Cebidae.  Mycetes — howling  monkey. 

Ateles — spider  monkey. 

Family  Cercopithecidae.     Cynocephalus — baboon. 

Macacus. 
Colobus. 

Family  Simiidae.     Hylobates — gibbon. 
Simia — orang. 
Gorilla. 

Anth  ropopithecus — chimpanzee. 
Family  Hominidae.     Homo — man. 
R.  4 


CHAPTER   III. 

SKELETON  OF  HEMICHORDATA,  UROCHORDATA, 
AND    CEPHALOCHORDATA. 

SXJBPHYLUM    A.    HEMICHORDATA. 

THE  subphylum  includes  three  genera,  Balanoglossus1,  Ce- 
phalodiscus  and  Rhabdopleura ;  and  perhaps  a  fourth,  Phoronis. 

The  skeletal  structures  found  in  Balanoglossus2  are  all 
endoskeletal.  They  include 

(1)  The  notochord.     This  arises  as  a  diverticuluni  from 
the  alimentary  canal  which  grows  forwards  into  the  proboscis 
and  extends  beyond  the    front    end  of    the    central    nervous 
system.     It  is  hypoblastic  in  origin  and  arises  in  the  same  way 
as  does  the  notochord  of  Ampkioxus.     Its  cells  become  highly 
vacuolated  and  take  on  the  typical  notochordal  structure3.     The 
cavity  of  the  primitive  diverticulum  becomes  obliterated  in  front, 
but  behind  it  opens  throughout  life  into  the  alimentary  canal. 

(2)  The  axial  skeletal  rods.     These  are  a  pair  of  chi- 
tinous  rods  which  lie  ventral  to  the  notochord  and  in  the  collar 
region  unite  to  form  a  single  mass. 

(3)  The  branchial  skeleton.     The  gill  bars  separating 
the  gill  slits  from  one  another  are  strengthened  by  chitinous 
rods  in   a  way  closely  similar   to   that   in  Ampliioxus,      But 
between  one  primary  forked  rod  and  the  next  there  are  two 
secondary  unforked  rods — not  one,  as  in  Amphioxus. 

(4)  The  chondroid  tissue.    This  is  of  mesoblastic  origin 
and  may  be  regarded  as  an  imperfect  sheath  for  the  notochord. 

In    Cephalodiscus  and  Rhabdopleura  as   in  Balanoglossus 

1  The  name  Balanoglossus  is  used  here  in  its  widest  sense  to  include 
all  the  Enteropneusta. 

2  See  W.  Bateson,  Quart.  J.  Micr.  Sci.  n.  s.  vol.  xxiv.  1884,  p.  208  and 
later;  also  E.  W.  Macbride,  Ibid.  vol.  xxxvi.  1894,  p.  385. 

3  See  p.  52. 


SKELETON   OF   UROCHORDATA   AND   CEPHALOCHORDATA.  51 ' 

the  notochord  forms  a  small  diverticulum  growing  forwards 
from  the  alimentary  canal  into  the  proboscis  stalk. 

Recent  researches  on  Phoronis1  show  the  existence  in  the 
collar  region  of  the  larva  (ActinotrocJia)  of  a  paired  organ, 
which  is  regarded  by  its  discoverer  as  representing  a  double 
notochord. 

SUBPHYLUM   B.   UROCHORDATA  (TUNICATA). 

Skeletal  structures  of  epiblastic  and  hypoblastic  origin 
occur  in  the  Urochordata.  Most  Tunicates  are  invested  by 
a  thick  gelatinous  test  which  often  contains  calcareous  spicules, 
and  serves  as  a  supporting  organ  for  the  soft  body.  The  cells 
of  this  test  are  mesodermal  in  origin. 

In  larval  Tunicata  and  in  adults  of  the  group  Larvacea 
the  tail  is  supported  by  a  typical  notochord,  which  is  confined 
to  the  tail.  In  all  Tunicata  except  Larvacea  all  trace  of 
the  notochord  is  lost  in  the  adult. 

SUBPHYLUM   C.    CEPHALOCHORDATA. 

This  subphylum  includes  the  well-known  genus  Amphioxus2. 


i 

5  8 

FIG.  3.     DIAGRAM  OF  THE  SKELETON  OF  Amphioxus  lanceolatus  x  3 
(after  a  drawing  in  the  Index  collection  at  the  Brit.  Mus.). 

1.  skeleton  of  dorsal  fin.  5.     branchial  skeleton. 

2.  notochord.  6.     septa   separating    the    myo 

3.  neural  tube.  tomes. 

4.  buccal  skeleton.  7.     skeleton  of  ventral  fin. 

In   Amphioxus  the  skeleton  is  very  simple.     It  contains  no 
trace  of   cartilage  or  bone  and  remains  throughout  life  in  a 

1  A.  T.  Masterman,  P.  R.  Soc.  Edinb.  1895—96,  p.  59  ;  and  Anat.  Anz. 
1896,  p.  266. 

2  See  E.  Ray  Lankester,  Quart.  J.  Micr.  Sci.  vol.  xxix.  n.  s.  1889,  p.  365. 
W.  B.  Benham,  Ibid.  vol.  xxxv.  n.  s.  1893,  p.  97.     J.  W.  Kirkaldy,  Ibid, 
vol.  xxxvn.  n.  s.  1895,  p.  303.     The  last-named  writer  divides  the  genus 
into  three  subgenera. 

4—2 


52  THE  VERTEBKATE  SKELETON. 

condition  corresponding  to  a  very  early  stage  in  Vertebrata. 
The  skeleton  of  Amphioxus  is  partly  hypoblastic,  partly  meso- 
blastic  in  origin. 

(a)  Hypoblastic  skeleton. 

The  notochord  (fig.  3,  2)  is  an  elastic  rod  extending  along 
the  whole  length  of  the  body  past  the  anterior  end  of  the 
nerve  cord.  It  lies  ventral  to  the  nerve  cord,  and  shows  no 
trace  of  segmentation.  It  is  chiefly  made  up  of  greatly  vacuo- 
lated  cells  containing  lymph,  but  near  the  dorsal  and  ventral 
surfaces  the  cells  are  less  vacuolated.  The  notochord  is  im- 
mediately surrounded  by  a  structureless  cuticular  layer,  the 
chordal  sheath,  and  outside  this  comes  the  mesoblastic  skeleto- 
genous  layer,  which  also  surrounds  the  nerve  cord. 

The  branchial  skeleton.  This  consists  of  a  series  of 
chitinous  elastic  rods  which  strengthen  the  gill  bars  and  are 
alternately  forked  and  unforked  ventrally.  The  forked  rods 
are  primary,  and  are  U-shaped  in  section,  the  unforked  rods 
are  secondary,  and  are  circular  in  section.  All  these  rods  are 
united  at  intervals  by  transverse  rods. 

(b)  Mesoblastic  skeleton. 

The  buccal  skeleton.  On  each  side  of  the  mouth  there 
is  a  curved  bar  resembling  the  notochord  in  structure.  The 
bars  are  segmented,  and  each  segment  bears  a  smaller  rod 
which  supports  a  tentacle,  the  whole  forming  the  buccal 
skeleton  (fig.  3,  4). 

The  notochord  is  enclosed  in  a  thick  sheath  of  connective 
tissue  continuous  with  a  thinner  sheath  round  the  nerve  cord. 
The  sheaths  of  the  notochord  and  nerve  cord  together  form  the 
skeletogenous  layer,  and  prolongations  of  it  form  the  myomeres 
or  septa  between  the  myotomes  or  segments  of  the  great  lateral 
muscles  of  the  body. 

The  skeleton  of  each  median  fin  consists  of  small 
cubical  masses  of  a  gelatinous  substance  arranged  in  rows 
(fig.  3,  1  and  7),  and  serving  to  strengthen  the  fins. 


CHAPTER   IV. 

SUBPHYLUM   D.   VERTEBRATA. 

THE  animals  included  in  this  great  group  all  possess  an 
internal  axial  skeleton  forming  the  vertebral  column  or  back- 
bone ;  and  a  dorsal  spinal  cord.  The  vertebral  column  is 
developed  from  the  skeletogenous  layer,  which  surrounds  the 
spinal  cord  together  with  the  notochord  and  its  sheath ;  and 
in  the  great  majority  of  cases  the  notochord  becomes  more  or 
less  modified  and  reduced  in  the  adult.  In  some  cases  the 
notochord  remains  unmodified  and  the  skeletogenous  layer 
surrounding  it  is  not  segmented  to  form  vertebrae,  but  in 
every  case  the  neural  arches  which  protect  the  spinal  cord 
are  segmented.  The  notochord  never  extends  further  forwards 
than  the  mid-brain. 

All  true  vertebrates  possess  a  cranium  or  skeletal  box 
enclosing  the  brain. 

(I.)     CYCLOSTOMATA. 

The  mouth  in  living  forms  is  suctorial  and  is  not  supported 
by  jaws.  In  some  fossil  forms  the  character  of  the  mouth  is 
unknown. 

Order  I.     MARSiPOBRANCHii1. 

In  these  animals  limbs  and  limb  girdles  are  always  com- 
pletely absent.  They  have  no  exoskeleton  except  horny  teeth. 

The  endoskeleton,  excluding  the  notochord,  is  entirely 
cartilaginous  or  membranous.  The  axial  skeleton  consists  of 
a  cartilaginous  cranium  without  jaws,  succeeded  by  a  thick 

1  See  W.  K.  Parker  On  the  skeleton  of  the  Marsipobranch  fishes, 
Phil.  Trans.  1883,  London. 


54  THE  VERTEBRATE  SKELETON. 

persistent  notochord  enveloped  in  a  sheath.  The  notochord 
in  living  forms  is  unsegmented,  but  segmented  cartilaginous 
neural  arches  are  present  in  some  cases.  A  complicated  series 
of  cartilaginous  elements  occurs  in  relation  to  the  mouth,  gills, 
and  sense  organs.  The  median  fins  are  supported  by  carti- 
laginous pieces,  the  radialia.  The  order  includes  the  Lampreys 
and  Hags. 

Order  II.     OsTRACODERMi1. 

The  forms  included  in  this  group  have  long  been  extinct, 
being  known  only  from  beds  of  Upper  Silurian  and  Lower 
Devonian  age.  They  differ  much  from  all  other  known  animals. 
The  exoskeleton  is  always  greatly  developed  and  includes 
(1)  large  bony  plates  covering  the  anterior  region;  (2)  scales 
covering  the  posterior  region.  The  plates  are  deeply  marked 
by  canals  belonging  to  dermal  sense  organs.  Jaws  are  un- 
known, and  arches  for  the  support  of  the  appendicular  skeleton 
are  rudimentary  or  absent.  The  tail  is  heterocercal  (see  p.  60). 

Suborder  (I).     HETEROSTRACI. 

The  exoskeleton  consists  principally  of  calcifications  form- 
ing dorsal  and  ventral  shields  which  cover  the  head  and  ab- 
dominal region;  the  dorsal  shield  is  formed  of  a  few  plates 
firmly  united,  the  ventral  shield  of  a  single  plate.  The  shields 
are  composed  of  three  layers,  the  middle  layer  being  traversed 
by  canals  belonging  to  the  dermal  sense  organs  which  open  to 
the  exterior  by  a  series  of  pores.  The  tail  is  sometimes  covered 
by  scales.  The  orbits  are  widely  separated  and  laterally 
placed.  Paired  appendages  are  absent.  These  curious  forms 
are  found  in  beds  of  Upper  Silurian  and  Lower  Devonian  age. 
One  of  the  best  known  genera  is  Pteraspis. 

Suborder  (2).     OSTEOSTRACI. 

The  exoskeleton  as  in  the  Heterostraci  consists  of  shields 
and  scales,  the  shields  being  divisible  into  three  layers.  The 

1  See  A.  Smith  Woodward,  Catalogue  of  Fossil  Fish'  in  the  British 
Museum,  Part  n.f  1891.  A.  Smith  Woodward,  Nat.  Sci.  vol.  i.  1892, 
p.  596. 


CYCLOSTOMATA.  55 

anterior  part  of  the  body  is  covered  dorsally  by  a  single  large 
shield  which  differs  from  those  of  the  Heterostraci  in  having 
the  inner  layer  ossified.  The  middle  layer  contains  canals  for 
the  passage  of  blood  vessels,  but  the  exoskeleton  shows  no 
impressions  of  dermal  sense  organs.  The  posterior  part  of  the 
body  is  covered  by  large  quadrangular  scales.  Paired  append- 
ages are  absent,  but  median  dorsal  and  caudal  fins  occur 
supported  by  scales,  not  fin-rays.  Cephalaspis,  the  best  known 
of  these  animals,  occurs  in  beds  of  Lower  Devonian  age. 

Suborder  (3).     ANTIARCHA. 

The  exoskeleton  is  formed  of  bony  plates,  the  dorsal  and 
ventral  shields  each  consisting  of  several  symmetrically  arranged 
pieces.  The  tail  may  be  covered  with  small  scales  or  may  be 
naked.  The  head  is  articulated  with  the  trunk,  and  its  angles 
are  drawn  out  into  a  pair  of  segmented  paddle-like  append- 
ages, covered  with  dermal  plates.  The  orbits  are  close  together. 
A  dorsal  fin  and  traces  of  mouth  parts  occur  in  Pterichthys, 
but  the  endoskeleton  is  unknown.  The  best  known  forms 
Pterichthys1  and  Aster olepis  occur  in  beds  of  Lower  Devonian 
age. 

GENERAL   ACCOUNT   OF   THE   SKELETON   OF 

MARSIPOBRANCHII. 

The  Marsipobranchii  are  worm-like  animals.  The  living 
forms  include  two  families,  the  Myxinoidei  (Hags) — genera 
Myxine  and  Bdellostoma — and  thePetromyzontidae  (Lampreys). 
Three  species  of  Petromyzon  are  known,  P.  fluviatilis,  P. 
marinus  and  P.  planeri.  The  larval  forms  were  for  a  long 
time  thought  to  belong  to  a  separate  genus  and  were  called 
Ammocoetes. 

The  Myxinoids,  although  very  highly  specialised  in  their 
own  way,  are  at  distinctly  a  lower  stage  of  development  than 
the  adult  Lamprey,  and  come  nearer  to  the  larval  Lamprey  or 
Ammocoete. 

1  See  B.  H.  Traquair,  Ann.  Nat.  Hist.,  ser.  6,  vol.  n.  1888,  p.  485. 


56 


THE  VERTEBRATE  SKELETON. 


SPINAL  COLUMN. 

In  Myxinoids  and  larval  lampreys,  the  notochord  is  en- 
closed in  a  thick  chordal  sheath,  in  connection  with  which  in 
the  tail  region  there  occur  cartilaginous  pieces  forming  neural 
arch  elements.  In  the  trunk  region,  however,  no  cartilage 
occurs  in  connection  with  the  spinal  column,  the  only  cartilage 
present  being  that  forming  the  radialia  of  the  dorsal  fin.  On 
the  other  hand  in  most  species  of  lamprey  (Petromyzon) 
cartilaginous  pieces  forming  imperfect  neural  arches  (fig.  4, 
B,  13)  are  found  lying  in  the  tough  skeletogenous  layer  dorsal 


FIG.  4.     A,  DORSAL  ;   B,  LATERAL  AND  C,  VENTRAL  VIEW  OF  THE 
SKULL  or  Petromyzon  marinus  x  1  (after  PARKER). 


1.  horny  teeth.  8. 

2.  labial  cartilage.  9. 

3.  anterior  dorsal  cartilage.  10. 

4.  posterior  dorsal  cartilage.  11. 

5.  nasal  capsule. 

6.  auditory  capsule.  12. 

7.  dorsal  portion  of  trabeculae.  13. 


lateral  distal  mandibular. 
lingual  cartilage, 
branchial  basket, 
cartilaginous  cup  supporting 

pericardium, 
sheath  of  notochord. 
neural  plate. 


to  the  notochord,  and  extending  throughout  the  whole  length 
of  the  trunk  and  tail.  Two  of  these  pieces,  which  are  probably 
homologous  with  the  neural  plates  (see  p.  72)  of  Elasmobranchs, 
occur  to  each  neuromere,  or  segment  as  determined  by  the 


CYCLOSTOMATA.  57 

spinal  nerves.  The  dorsal  and  caudal  fins  are  supported  by 
paired  cartilaginous  radialia  which  are  connected  proximally 
with  the  skeletogenous  layer. 

THE  SKULL. 

In  Myxinoids  the  cranium  is  a  mere  cartilaginous  floor 
without  side  walls  or  roof,  and  the  trabeculae1  end  without 
growing  forwards  into  cornua.  In  Lampreys  the  trabeculae 
grow  forwards  and  send  up  plates  of  cartilage  which  meet 
above  (fig.  4,  7)  and  form  side  walls  and  a  roof  for  part  of  the 
brain  case.  In  Lampreys  a  labial  suctorial  apparatus  is  well 
developed,  including  a  large  ring-like  piece  of  cartilage  (fig.  4,  2) 
which  supports  the  oral  funnel  and  bears  a  large  armament  of 
horny  teeth.  In  Myxinoids  on  the  other  hand  the  labial 
skeleton  is  small  and  consists  merely  of  barbels  round  the 
mouth. 

The  olfactory  organ  of  Myxinoids  has  a  very  curious 
skeleton.  It  is  covered  with  a  kind  of  grating  of  cartilage 
which  is  prolonged  in  front  into  a  tube  composed  of  a  series  of 
imperfect  cartilaginous  rings.  In  Lampreys  the  olfactory 
organ  opens  merely  by  a  short  membranous  passage.  In 
correlation  with  the  small  development  of  the  labial  suctorial 
apparatus  in  Myxinoids  the  lingual  apparatus  is  very  greatly 
developed.  The  tongue  in  Myxine  has  been  said  to  'dominate 
the  whole  body'  (Parker).  It  is  supported  by  a  great  median 
cartilaginous  bar  which  when  followed  forwards  first  becomes 
bifid  and  still  further  forwards  becomes  four-cleft. 

The  horny  teeth  in  Myxinoids  are  chiefly  borne  on  the 
very  large  supralingual  apparatus.  They  form  a  double  series 
arranged  in  the  form  of  an  arch.  In  Myxine  there  are  seven 
large  teeth  and  nine  small  ones  on  each  side.  In  Bdellostoma 
the  teeth  of  the  two  rows  are  more  equal  in  size.  In  Bdello- 
stoma and  Myxine  it  has  been  shown  that  imperfect  calcified 
teeth  occur  below  the  horny  teeth. 

1  See  p.  17. 


58  THE  VERTEBRATE  SKELETON. 

In  Lampreys  the  lingual  apparatus  (fig.  4,  C,  9)  is  well  de- 
veloped, but  not  excessively  so.  It  consists  of  a  long  median 
cartilaginous  bar  which  ends  in  front  with  a  semicircular  piece 
of  cartilage  supporting  the  median  part  of  the  tongue. 

In  both  Myxinoids  and  Lampreys  there  is  a  complicated 
branchial  basket  apparatus,  but  while  in  Myxinoids  the  basket 
apparatus  is  interbranchial,  formed  deep  within  the  head 
near  the  hypoblastic  lining  of  the  throat,  in  Lampreys  it  is 
extra -branchial  and  formed  outside  the  head  cavities  (fig. 
4,  10).  The  two  sides  of  the  basket  apparatus  in  Myxine  are 
not  symmetrical.  In  the  interbranchial  basket  apparatus  of 
Myxinoids  the  hyoid  and  first  and  second  branchial  arches 
can  be  recognised.  Traces  of  the  interbranchial  skeleton  of 
Myxinoids  can  be  detected  in  Lampreys,  and  similarly  in 
Myxinoids,  there  are  indications  of  the  extrabranchial  skeleton 
of  Petromyzon.  The  branchial  basket  in  Lampreys  forms  at 
its  posterior  end  a  kind  of  cup  which  supports  the  pericardium 
(fig.  4,  11). 

A  remarkable  Cyclostome  named  Palaeosj)ondylusl  has  re- 
cently been  described  from  the  Scottish  Old  Red  Sandstone. 
It  differs  however  from  all  living  Cyclostomes,  in  having  a 
spinal  column  formed  of  distinct  vertebrae  with  well-developed 
neural  arches.  The  caudal  fin  is  well  developed  and  the  dorsal 
radialia  are  forked  as  in  lampreys.  The  skull  is  well  calcified 
and  the  auditory  capsules  are  specially  large.  The  mouth  is 
very  similar  to  that  of  lampreys,  being  circular  and  without 
jaws ;  it  is  provided  with  barbels  or  cirri.  There  is  no  trace 
of  limbs  and  the  average  length  is  only  about  1 — 1J  inches. 

1  R.  H.  Traquair,  Ann.  Nat.  Hist.  vol.  vi.  1890,  p.  485  ;  P.  Phys.  Soc. 
Edinb.  vol.  xn.  1892—93,  pp.  87—94,  and  312—320.  A.  Smith  Woodward, 
Nat.  Sci.  vol.  in.  p.  128,  1893. 


CHAPTER   V. 
(II. )     GN  ATHOSTOM  AT  A. 

THE  mouth  is  supported  by  definite  jaws. 

ICHTHYOPSIDA. 

The  epiblastic  exoskeleton  is  generally  unimportant,  the 
mesoblastic  exoskeleton  is  usually  well  developed. 

The  notochord  with  its  membranous  sheath  (1)  may  remain 
unmodified,  or  (2)  may  be  replaced  by  bone  or  cartilage  derived 
from  the  skeletogenous  layer,  or  (3)  may  be  calcified  to  a 
varying  extent. 

The  first  vertebra  is  not  homologous  throughout  the  whole 
series  and  so  is  not  strictly  comparable  to  the  atlas  of  Saur- 
opsids  and  Mammals. 

The  centra  of  the  vertebrae  have  no  epiphyses.  The 
skull  may  be  (a)  incomplete  and  membranous,  or  (6)  more  or 
less  cartilaginous,  or  (c)  bony.  Membrane  bones  are  not 
included  in  the  cranial  walls,  and  there  are  large  unossified 
tracts  in  the  skull.  When  membrane  bones  are  developed  in 
connection  with  the  skull,  a  large  parasphenoid  occurs.  The 
basisphenoid  is  always  small  or  absent.  The  skull  may  be 
immovably  fixed  to  the  vertebral  column,  or  may  articulate 
with  it  by  a  single  or  double  occipital  condyle.  When  the 
occipital  condyle  is  double,  it  is  formed  by  the  exoccipitals, 
and  the  basi- occipital  is  small  or  unossified.  The  mandible 
may  be  (a)  cartilaginous,  (b)  partially  ossified,  or  (c)  membrane 
bones  may  be  developed  in  connection  with  it, — if  so,  there  is 


60  THE  VERTEBRATE  SKELETON. 

usually  more  than  one  membrane  bone  developed  in  connection 
with  each  half. 

There  are  at  least  four  pairs  of  branchial  arches  present 
during  development.  The  sternum,  if  present,  is  not  costal 
in  origin. 

CLASS  I.     PISCES. 

The  exoskeleton  is  in  the  form  of  scales,  which  may  be 
entirely  mesoblastic  or  dermal  in  origin  (e.g.  cycloid  and 
ctenoid  scales),  or  may  be  formed  of  both  mesoblast  and  epi- 
blast  (e.g.  placoid  and  ganoid  scales).  Large  bony  plates  may 
be  derived  from  both  these  types  of  scale.  In  general  fish 
with  a  greatly  developed  dermal  armour  have  the  endoskeleton 
poorly  developed;  and  the  converse  also  holds  good. 

The  integument  of  the  dorsal  and  ventral  surfaces  is 
commonly  prolonged  into  longitudinal  unpaired  fins,  sup- 
ported by  an  internal  skeleton.  These  fins  are  distinguished 
according  to  their  position  as  dorsal,  caudal  and  anal  fins. 
The  dorsal  and  anal  fins  are  used  chiefly  as  directing  organs, 
the  caudal  fin  is  however  a  most  important  organ  of  pro- 
pulsion. 

Three  types  of  tail  are  found  in  fishes,  viz. : — 

1.  The  diphycercal,  in  which  the  axis  is  straight  and 
the  tail  is  one-bladed  and  symmetrical,  an  equal  proportion  of 
radialia1  being  attached  to  the  upper  and  lower  surfaces  of  the 
axis. 

2.  The  heterocercal,  in  which  the  tail  is  asymmetrical 
and  the  axis  is  bent  upwards,  the  proportion  of  radialia  or  of 
fin-rays  attached  to  its  upper  surface  being  much  smaller  than 
that  attached  to  its  lower  surface. 

3.  The   home-cereal,   in  which   the   tail   though  ex- 
ternally symmetrical,  so  far  resembling  the  diphycercal  type,  is 
internally  really  heterocercal,  the  great  majority  of  the  radialia 
or  of  the  fin-rays  being  attached  to  the  lower  surface  of  the  axis. 

1  See  p.  79. 


PISCES.  61 

The  cranium  in  the  simplest  cases  (e.g.  Selachii)  forms  a 
cartilaginous  box  enclosing  the  brain  and  sense  organs ;  in 
bony  fishes  it  is  greatly  complicated.  When  palatine  or 
pterygoid  bones  are  present  they  are  formed  by  the  ossifi- 
cation of  cartilage ;  in  Sauropsida  and  Mammalia  they  are 
laid  down  as  membrane  bones.  There  is  no  tympanic  cavity 
or  auditory  ossicle  in  relation  to  the  ear. 

There  are  two  principal  types  of  suspensorium  by  means  of 
which  the  jaws  are  attached  to  the  cranium  : — 

(1)  The  Autostylic.     This  is  the  primitive  condition 
in  which  the  mandibular  arch  articulates  with  the  base  of  the 
cranium  in  front  of  the  hyoid  and  in  a  similar  manner. 

(2)  The  Hyostylic.     In  this  case  the  mandibular  arch 
becomes  connected  with  the  hyomandibular  and  supported  by 
the   hyoid   arch.     These  terms  are  more   fully  discussed   in 
Chapter  VIII. 

There  is  always  an  internal  framework  supporting  the 
gills ;  it  usually  consists  of  the  hyoid  arch  and  five,  rarely 
six  or  seven,  pairs  of  branchial  arches.  The  limbs  are  repre- 
sented by  two  pairs  of  fins,  the  pectoral  and  the  pelvic ;  they 
are  not  divided  into  proximal,  middle  and  distal  portions.  The 
ribs  do  not  unite  with  a  median  ventral  sternum,  or  meet  in 
the  midventral  line  in  any  other  way  in  the  trunk  region. 

Order  I.     ELASMOBRANCHII. 

The  exoskeleton  is  in  the  form  of  placoid  scales  which  are 
sometimes  so  numerous  as  to  give  the  whole  skin  a  rough 
surface  forming  shagreen.  In  some  cases  the  placoid  scales 
are  enlarged  to  form  plates  or  spines  capped  or  coated  with 
enamel.  These  spines  may  be  imbedded  in  the  flesh  in  front 
of  the  paired  or  unpaired  fins,  or  may  be  attached  to  the  tail. 
They  are  specially  characteristic  of  the  suborder  Acanthodii. 
The  endoskeleton  is  cartilaginous  and  true  bone  is  never 
found.  Much  of  the  skeleton,  especially  of  the  vertebral 


62  THE  VERTEBRATE  SKELETON. 

column,  is  however  often  calcined,  this  being  especially  well 
seen  in  the  anterior  part  of  the  vertebral  column  of  Rays 
(Raiidae).  In  living  forms  cartilaginous  biconcave  vertebrae 
are  always  well  developed,  but  in  some  extinct  forms  the 
notochord  persists  unconstricted.  Neural  and  haemal  arches 
are  however  always  developed ;  they  sometimes  remain 
separate,  sometimes  fuse  with  the  centra.  Ribs  are  often 
wanting  and  when  present  are  often  not  separated  off  from  the 
vertebrae.  The  cranium  is  a  simple  cartilaginous  box  whose 
most  prominent  parts  are  the  capsules  which  enclose  the 
sense  organs.  The  skull  is  sometimes  immovably  fixed  to 
the  vertebral  column,  sometimes  articulates  with  it  by  means 
of  two  condyles.  There  is  no  operculum  and  no  representative 
of  the  maxilla  or  premaxilla.  The  teeth  are  very  variable. 
Large  pectoral  and  pelvic  fins  always  occur. 

The  Elasmobranchii  may  be  divided  into  four  suborders : — 

(1)  Ichthyotomi. 

(2)  Pleuropterygii. 

(3)  Selachii. 

(4)  Acanthodii. 

Suborder  (1).     ICHTHYOTOMI  \ 

The  members  of  this  suborder  range  from  the  Devonian  to 
the  Permian  and  so  have  long  been  extinct. 

The  endoskeletal  cartilage  has  granular  calcifications  evenly 
distributed  throughout  it.  The  notochord  is  unconstricted,  but 
the  neural  and  haemal  arches  are  well-developed,  and  the 
neural  spines  are  long  and  slender.  There  is  a  continuous 
dorsal  fin  with  separate  basalia  and  radialia.  The  tail  is  di- 
phycercal,  and  the  pectoral  fins  are  typical  archipterygia -. 
The  pelvic  fins  of  the  male  are  prolonged  to  form  claspers. 

1  For  this  arid  other  groups  of  extinct  fish  see  A.  Smith  Woodward, 
Catalogue  of  Fossil  Fish  in  the  British  Museum,  Parts  i. — in.     London, 
1889—95. 

2  See  p.  127. 


PISCES.      ELASMOBRANCHII.  63 

The  best  known  of  these  primitive  Elasmobranchs  are  the 
Pleuracanthidae. 

Suborder  (2).     PLEUROPTERYGII. 

This  suborder  was  formed  for  the  reception  of  Cladoselache, 
an  Elasmobranch  found  in  the  Lower  Carboniferous  of  Ohio1. 

The  exoskeleton  is  in  the  form  of  small,  thickly-studded 
dermal  denticles.  The  vertebral  centra  are  unossified,  and 
the  tail  is  strongly  heterocercal.  There  were  certainly  five, 
perhaps  seven  gill  slits,  and  the  suspensorium  is  apparently 
hyostylic.  The  paired  fins  are,  according  to  the  view  which 
derives  them  by  concentration  from  continuous  lateral  folds, 
the  most  primitive  known  (see  p.  129)  and  claspers  are 
absent. 

Suborder  (3).     SELACHII. 

Cartilaginous  or  partially  calcified  biconcave  vertebrae  are 
always  well  developed ;  they  constrict  the  notochord  inter- 
vertebrally.  The  neural  and  haemal  arches  and  spines  are 
stout  and  intercalary  cartilages  (interdorsalia)  are  present. 
The  tail  is  heterocercal,  but  in  some  cases  (Squatina)  ap- 
proaches the  diphycercal  condition.  In  most  cases  the  suspen- 
sorium is  hyostylic,  the  jaws  being  attached  to  the  cranium 
by  means  of  the  hyomandibular,  and  the  palato-pterygo- 
quadrate  bar  not  being  fused  to  the  cranium.  There  are 
generally  five  pairs  of  branchial  arches,  and  gill  rays  are 
borne  on  the  posterior  surface  of  the  hyoid  arch,  and  on  both 
the  anterior  and  posterior  surfaces  of  the  first  four  branchial 
arches.  The  J^otidanidae  differ  from  most  Selachians  in  two 
respects,  first  as  regards  the  suspensorium, — Meckel's  cartilage 
articulating  directly  with  the  palato-pterygo-quadrate  bar,  and 
not  being  connected  with  the  hyoid  arch ;  and  secondly  as 
regards  the  number  of  branchial  arches, — six  pairs  occurring 
in  Hexanchus  and  seven  in  Heptanchus. 

The  pectoral  fins  are  without  the  segmented  axis  of  the 
1  See  B.  Dean,  J.  MorphoL  vol.  ix.  pp.  87—114,  1894,  and  Nat.  Sci. 
voL  vin.  p.  245,  1896. 


64  THE  VERTEBRATE  SKELETON. 

archipterygium.  In  most  cases  they  are  sharply  marked  off 
from  the  body  and  lie  almost  at  right  angles  to  it ;  but  in  the 
Rays  they  have  the  form  of  lateral  expansions  in  the  same 
plane  as  the  body,  from  which  they  are  not  sharply  marked 
off.  The  pelvic  fins  in  the  male  bear  long  grooved  cartilaginous 
rods  which  are  accessory  copulatory  organs  or  claspers. 

There  are  two  principal  groups  of  Selachii,  the  Squalidae 
or  Sharks  aijd  Dogfish,  and  the  Batoidei  or  Skates  and  Rays. 
The  Squalidae  have  the  shape  of  ordinary  fish,  the  pectoral 
fins  are  vertically  placed  and  the  body  ends  in  a  powerful 
heterocercal  tail.  The  Batoidei  have  flattened  bodies  owing 
to  the  great  size  and  horizontal  position  of  the  pectoral  fins. 
The  tail  is  long  and  thin  and  is  often  armed  with  spines. 
The  teeth  in  Selachii  differ  much  in  character  in  the  different 
forms,  and  are  always  arranged  in  numerous  rows.  They  are 
generally  pointed  and  triangular  or  conical  in  the  Squalidae, 
while  in  the  Batoidei  they  are  often  broad  and  flattened. 

Suborder  (4).     ACANTHODII. 

The  fishes  included  in  this  group  are  all  extinct  and 
in  some  respects  are  intermediate  between  Elasmobranchii 
and  Gaiioidei.  The  body  is  elongated  and  closely  covered 
with  small  scales  consisting  of  dentine  enamelled  at  the  sur- 
face. The  notochord  is  persistent  and  the  calcification  of  the 
endoskeletal  cartilage  is  only  superficial.  The  tail  is  hetero- 
cercal. The  jaws  bear  small  conical  teeth,  or  in  some  cases 
are  toothless.  The  skeleton  of  all  the  fins  differs  from  that  of 
modern  Elasmobranchs  in  having  the  cartilaginous  radialia 
much  reduced,  and  the  fins  are  nearly  always  each  provided 
with  an  anterior  spine,  which  except  in  the  case  of  the  pec- 
toral fins  is  merely  inserted  between  the  muscles.  These  spines 
are  really  enormous  dermal  fin-rays ;  the  pectoral  fin-spine  is 
articulated  to  the  pectoral  girdle. 

The  suborder  includes  many  well-known  extinct  forms  like 
Acanthodes  and  Diplacanthus ;  it  ranges  from  the  Devonian  to 
the  Permian. 


PISCES.      HOLOCEPHALI. 


65 


Order  II.     HOLOCEPHALI. 
This  order  includes  a  single  suborder  only. 
Suborder.     CHIMAEROIDEI. 

These  singular  fish  have  the  skin  smooth  and  in  living 
forms  almost  or  quite  scaleless.  The  palato-pterygo-quadrate 
bar  and  hyomandibular  are  fused  to  the  cranium,  and  Meckel's 
cartilage  articulates  directly  with  the  part  corresponding  to  the 
quadrate.  The  skull  is  distinctly  articulated  with  the  spinal 


10, 


FIG.  5.     SKULL  OF  A  MALE  Chimaera  monstrosa  (after  HUBBECHT). 


1.  nasal  capsule. 

2.  cartilaginous  appendage    to 
the  fronto-nasal  region. 

3.  erectile  appendage. 

4.  foramen  by  which  the  oph- 
thalmic nerves  leave  the  orbit. 

5.  foramen  by  which  the  oph- 
thalmic branch  of  the  Vth  nerve 
enters  the  orbit. 


6.  auditory  capsule. 

7.  interorbital  septum. 

8.  mandible    articulating   with 
an   outgrowth   from  the  posterior 
part  of  the  palato-pterygo-quadrate. 

9.  teeth. 

10.     labial  cartilage. 
II.  III.  V.  VII.  IX.  X.  foramina 
for  the  passage  of  cranial  nerves. 


column,  the  notochord  is  persistent  and  unconstricted,  and  the 
skeletogenous  layer  shows  no  trace  of  metameric  segmentation, 

K.  5 


66  THE  VERTEBRATE  SKELETON. 

though  in  the  neural  arches  this  segmentation  is  readily  trace- 
able. The  neural  arches  of  the  first  few  vertebrae  are  fused 
together  and  completely  surround  the  notochord,  while  they 
do  not  in  other  parts  of  the  body.  The  tail  is  diphy cereal. 
Of  the  living  genera,  in  Callorhynchus  there  is  no  trace  of 
calcification  in  the  skeletogenous  layer,  while  in  Chimaera  rings 
of  calcification  are  found,  there  being  three  to  five  for  each 
vertebra  as  indicated  by  the  foramina  for  the  exit  of  the  spinal 
nerves.  The  pelvic  fins  are  produced  into  claspers.  Besides 
the  living  genera  Chimaera,  Harriotta  and  Callorhynchus  a 
fair  number  of  fossil  forms  are  known,  e.g.  Ischyodus. 

Order  3.     GANOIDEI. 

The  fishes  included  under  the  term  Ganoidei  form  a  very 
heterogeneous  group,  some  of  which  closely  approach  the  Dipnoi, 
others  the  Elasmobranchii,  others  the  Teleostei.  The  great 
majority  of  them  are  extinct,  only  eight  living  genera  being 
known;  these  are  all  inhabitants  of  the  northern  hemisphere, 
and  with  the  exception  of  Acipenser,  which  is  both  fluviatile 
and  marine,  are  entirely  confined  to  fresh  water. 

The  following  is  a  list  of  the  living  genera  of  Ganoids  with 
their  respective  habitats : — 

Acipenser.     Rivers  and  seas  of  the  northern  hemisphere. 

Scaphirhynchus.     Mississippi  and  rivers  of  Central  Asia. 

Polyodon  (Spatularia).     Mississippi. 

Psepkurus.     Yan-tse-kiang,  and  Hoangho. 

Polypterus.     Rivers  of  tropical  Africa. 

Calamoichthys.     Some  rivers  of  West  Africa. 

Lepidosteus.    Freshwaters  of  Central  and  North  America 
and  Cuba. 

Amia.     Rivers  of  Carolina. 

The  exoskeleton  is  very  variable,  thus  the  body  may  be : — 

(a)     Naked  or  with  minute  stellate  ossifications  as  in 

the  Polyodontidae.     (b)    Partially  covered  with  large  detached 


PISCES.      GANOIDEI.  67 

bony  plates  as  in  Scaphirhynchus  and  Acipenser.  (c)  Entirely 
covered  with  rhomboidal  ganoid  scales  as  in  Lepidosteus, 
Polypterus,  Palaeoniscus  and  many  extinct  forms,  (d)  Covered 
with  rounded  scales  shaped  like  the  cycloid  scales  of  Teleosteans 
as  in  Amia.  (e)  Having  the  trunk  and  part  of  the  tail  covered 
with  rhomboidal  scales,  and  the  remainder  of  the  tail  with 
rounded  scales  as  in  Trissolepis. 

The  teeth  also  are  very  variable.  The  endoskeleton  shows 
every  stage  of  transition  from  an  almost  entirely  cartilaginous 
state  as  in  Acipenser  to  a  purely  bony  state  as  in  Lepidosteus. 
Sometimes,  as  in  Acipenser,  the  notochord  persists,  and  its 
sheath  is  unsegmented ;  sometimes,  as  in  Lepidosteus,  there 
are  fully  formed  vertebrae.  The  tail  may  be  heterocercal,  as 
in  Acipenser,  or  diphy cereal  as  in  Polypterus.  The  cartila- 
ginous cranium  is  always  covered  with  external  membrane 
bone  to  a  greater  or  less  extent,  and  the  suspensorium  is 
markedly  hyostylic.  The  pectoral  girdle  is  formed  of  two 
parts,  one  endoskeletal  and  cartilaginous,  corresponding  with 
the  pectoral  girdle  of  Elasmobranchs,  and  one  exoskeletal 
and  formed  of  membrane  bones,  corresponding  with  the  cla- 
vicular bones  of  Teleosteans.  The  pelvic  fins  are  always 
abdominal.  The  fins  often,  as  in  Polypterus,  have  spines 
(fulcra)  attached  to  their  anterior  borders. 

The  order  Ganoidei  may  be  divided  into  three  suborders  : 

(1)  CHONDROSTEI.      Living    genera   Acipenser,    Scaphi- 
rhynchus, Polyodon  and  Psephurus. 

(2)  CROSSOPTERYGII.     Living    genera  Polypterus.   and 
Calamoichthys. 

(3)  HOLOSTEI.     Living  genera  Lepidosteus  and  Amia. 

Suborder  (1).     CHONDROSTEI. 

The  skull  is  immovably  fixed  to  the  vertebral  column. 
By  far  the  greater  part  of  the  skeleton  is  cartilaginous. 
The  notochord  is  persistent  and  unconstricted,  its  sheath  is 
membranous,  but  cartilaginous  neural  and  haemal  arches  are 

5—2 


68  THE  VERTEBRATE  SKELETON. 

developed.  Intercalary  pieces  (interdorsalia)  occur  between 
the  neural  arches,  and  similar  pieces  (interventralia)  between 
the  haemal  arches.  The  cranium  is  covered  with  membrane 
bone,  and  teeth  are  but  slightly  developed.  The  tail  is  hetero- 
cercal.  Gill  rays  occur  on  the  hyoid  arch,  and  the  gills  are 
protected  by  a  bony  operculum  attached  to  the  hyomandi- 
bular.  The  skin  (1)  may  be  almost  or  quite  naked,  (2)  may 
carry  bony  plates  arranged  in  rows,  or  may  be  covered  (3)  with 
rhomboidal  scales,  or  (4)  partly  with  rhomboidal,  partly  with 
cycloidal  scales. 

Suborder  (2).     CROSSOPTERYGII. 

The  exoskeleton  has  the  form  of  cycloidal  or  rhomboidal 
scales.  The  condition  of  the  vertebral  column  differs  in  the 
different  genera.  Sometimes,  as  in  Polypterus,  there  are  well- 
developed  ossified  vertebrae;  sometimes,  as  in  many  extinct 
forms,  the  notochord  persists  and  is  unconstricted.  The  tail 
may  be  diphycercal  *or  heterocercal.  The  pectoral  and  some- 
times the  pelvic  fins  consist  of  an  endoskeletal  axis  bearing 
a  fringe  of  dermal  rays. 

Suborder  (3).     HOLOSTEI. 

The  exoskeleton  has  the  form  of  cycloidal  or  rhomboidal 
scales.  The  notochord  is  constricted  and  its  sheath  is  seg- 
mented and  ossified,  forming  distinct  vertebrae,  which  are 
generally  biconcave,  sometimes  opisthocoelous  (Lepidosteus) . 
The  cartilaginous  cranium  is  largely  replaced  by  bone,  and  in 
connection  with  it  we  find  not  only  membrane  bone,  but 
cartilage  bone,  as  the  basi-occipital,  exoccipitals,  and  pro- otic 
are  ossified.  The  tail  is  heterocercal.  The  suspensorium 
resembles  that  of  Teleosteans,  consisting  of  a  proximal  ossifi- 
cation, the  hyomandibular,  which  is  movably  articulated  to 
the  skull  and  a  distal  ossification,  the  symplectic.  The  two 
are  separated  by  some  unossified  cartilage.  The  cartilaginous 
upper  and  lower  jaws  are  to  a  great  extent  surrounded  and 
replaced  by  a  series  of  membrane  bones. 


PISCES.      TELEOSTEI.  69 

Order  4.     TELEOSTEI. 

The  exoskeleton  is  sometimes  absent  but  generally  consists 
of  overlapping  cycloid  or  ctenoid  scales.  Bony  plates  are  some- 
times present,  as  in  the  Siluridae,  or  the  body  may  be  encased 
in  a  complete  armour  of  calcined  plates,  as  in  Ostracion. 
Enamel  is  however  never  present,  and  the  plates  are  entirely 
mesodermal.  The  skeleton  is  bony,  but  in  the  skull  much 
cartilage  generally  remains.  The  vertebral  centra  are  usually 
deeply  biconcave,  and  the  tail  is  of  the  masked  heterocercal 
type  distinguished  as  homocercal.  In  the  skull  the  occipital 
region  is  always  completely  ossified,  while  the  sphenoidal 
region  is  generally  less  ossified.  The  skull  has  usually 
a  very  large  number  of  membrane  bones  developed  in  connec- 
tion with  it.  The  teeth  vary  much  in  character  in  the  different 
members  of  the  order,  but  are  as  a  rule  numerous  and  pointed, 
and  are  ankylosed  to  the  bone.  The  suspensorium  is  hyo- 
stylic  and  the  jaws  have  much  the  same  arrangement  as  in 
the  Holostei.  There  are  five  pairs  of  branchial  arches,  of 
which  all  except  the  last  bear  gill  rays.  A  series  of  dermal 
opercular  bones  is  developed  in  connection  with  these  arches. 
The  pectoral  girdle  consists  almost  entirely  of  dermal  clavicular 
bones.  The  pelvic  girdle  has  disappeared,  its  place  being  taken 
by  the  enlarged  and  ossified  dermal  fin-rays  of  the  pelvic  fins. 

The  group  includes  the  vast  majority  of  living  fish  (see 
p.  33). 

Order  5.     DIPNOI. 

The  exoskeleton  is  of  two  types ;  dermal  bones  are  largely 
developed  in  the  head  region,  while  the  tail  and  posterior 
part  of  the  body  may  be  naked  or  may  be  covered  with  over- 
lapping scales.  The  cranium  remains  chiefly  cartilaginous, 
the  palato-pterygo-quadrate  bar  is  fused  with  the  cranium, 
and  the  suspensorium  is  autostylic.  The  gill  clefts^  are  feebly 
developed  and  open  into  a  cavity  covered  by  an  operculum. 
The  notochord  is  persistent  and  unconstricted,  and  the  limbs 
are  archipterygia.  The  pelvic  fins  are  without  claspers. 


70  THE   VERTEBRATE   SKELETON. 

Suborder  (1).      SiRENOiDEi1. 

The  head  has  well  developed  membrane  bones.  The  trunk 
is  covered  with  overlapping  scales  and  bears  no  bony  plates. 
Three  pairs  of  teeth  are  present,  two  in  the  upper  and  one 
in  the  lower  jaw,  the  two  principal  pairs  of  teeth  are  borne  on 
the  palato-pterygoids  and  splenials,  while  the  third  pair  are 
found  in  the  vomerine  region.  The  tail  is  diphycercal  in 
living  forms.  In  the  extinct  Dipteridae  it  is  heterocercal. 
The  pectoral  girdle  includes  both  membrane  and  cartilage 
bones.  The  pelvic  girdle  consists  of  a  single  bilaterally 
symmetrical  piece  of  cartilage. 

This  suborder  is  represented  by  the  living  genera  Ceratodus, 
Protopterus  and  Lepidosiren,  and  among  extinct  forms  by  the 
Dipteridae  and  others. 

Suborder  (2).     ARTHRODIRA. 

Bony  plates  are  developed  not  only  on  the  head  but  also 
on  the  anterior  part  of  the  trunk,  where  they  consist  of  a 
dorsal,  a  ventral,  and  a  pair  of  lateral  plates  which  articulate 
with  the  cranial  shield.  The  posterior  part  of  the  trunk  is 
naked.  The  tail  is  diphycercal.  The  jaws  are  shear-like,  and 
their  margins  are  usually  provided  with  pointed  teeth  whose 
bases  fuse  with  the  tissue  of  the  jaw  and  constitute  dental 
plates.  There  seem  to  have  been  three  pairs  of  these  plates, 
arranged  as  in  the  Sirenoidei,  the  principal  ones  in  the  upper 
jaw  being  borne  on  the  palato-pterygoids.  Small  pelvic  fins 
are  present,  but  pectoral  fins  are  unknown. 

The  Arthrodira  occur  chiefly  in  beds  of  Devonian  and 
Carboniferous  age.  Two  of  the  best  known  genera  are 
Coccosteus  from  the  European  Devonian  and  Dinichthyx,  a 
large  predatory  form  from  the  lower  Carboniferous  of  Ohio. 

1  A.  Giinther,  Phil.  Trans,  vol.  161,  Part  11.  1871,  p.  511.  T.  H. 
Huxley,  "On  Ceratodus  and  the  classification  of  fishes,"  P.Z.S.  1876, 
p.  24. 


CHAPTER  VI. 

THE   SKELETON    OF   THE   DOGFISH1. 

Scyllium   canicula. 

I.  EXOSKELETON. 

The  exoskeleton  of  the  dogfish  is  mainly  composed  of  placoid 
scales,  each  of  which  consists  of  a  little  bony  base  imbedded 
in  the  skin,  bearing  a  small  backwardly-directed  spine  formed 
of  dentine  capped  with  enamel.  The  scales  are  larger  on 
the  dorsal  than  on  the  ventral  surface,  and  on  the  jaws  they 
are  specially  large  and  regularly  arranged  in  rows,  there 
forming  the  teeth.  The  margins  of  the  jaws  or  lips  are  with- 
out scales. 

A  second  exoskeletal  structure  is  found  in  the  fins,  all 
of  which,  both  paired  and  unpaired,  have,  in  addition  to  their 
cartilaginous  endoskeleton,  large  numbers  of  long  slender 
horny  fibres,  the  fin-rays,  which  are  of  exoskeletal  origin. 

II.  ENDOSKELETON. 

The  endoskeleton  of  the  dogfish  consists  almost  entirely 
of  cartilage,  which  however  may  become  calcified  in  places, 
e.g.  the  centrum  of  each  vertebra  is  lined  by  a  layer  of  calcified 
tissue. 

The  endoskeleton  is  divisible  into  an  axial  portion  con- 
sisting of  the  vertebral  column,  skull,  and  skeleton  of  the 
median  fins,  and  an  appendicular  portion  consisting  of  the 
skeleton  of  the  paired  fins  and  their  girdles. 

1  See  Marshall  and  Hurst's  Practical  Zoology,  4th  ed.  London,  1895, 
p.  214. 


72  THE   VERTEBRATE    SKELETON. 

1.     THE  AXIAL  SKELETON. 
A.     THE  VERTEBRAL  COLUMN  AND  RIBS. 

The  vertebral  column  consists  of  a  series  of  some  hundred 
and  thirty  vertebrae,  each  of  which  is  united  with  its  pre- 
decessor and  successor  in  such  a  way  as  to  allow  a  large 
amount  of  flexibility. 

These  vertebrae  are  developed  round  an  unsegmented 
rod,  the  notochord,  which  forms  the  axial  support  of  the 
embryo.  The  notochord  remains  continuous  throughout  the 
whole  vertebral  column,  but  is  greatly  constricted  opposite  the 
middle  of  each  vertebra,  and  thus  rendered  moniliform.  The 
vertebrae  are  divided  into  two  groups,  an  anterior  group  of 
trunk  vertebrae,  and  a  posterior  group  of  caudal  or  tail 
vertebrae. 

A  typical  vertebra  consists  of  a  middle  portion,  the  cen- 
trum, a  dorsal  portion,  the  dorsal  or  neural  arch,  which 
surrounds  the  spinal  cord,  and  a  ventral  portion,  the  ventral 
or  haemal  arch,  which  similarly  encloses  a  space. 

The  tail  vertebrae  of  the  dogfish  have  this  typical  arrange- 
ment, the  trunk  vertebrae  have  the  haemal  arches  modified. 

Each  centrum  is  a  short  cylinder  of  cartilage  surrounding 
an  hourglass-shaped  cavity  occupied  by  the  notochord.  The 
neural  arches  are  composed  of  three  separate  elements,  the 
vertebral  neural  plates  (basidorsalia),  intervertebral 
neural  plates  (interdorsalia),  and  neural  spines  (supra- 
dorsalia). 

The  vertebral  neural  plates  are  in  the  adult  fused  with 
their  respective  centra,  and  are  notched  behind  for  the  exit 
of  the  ventral  (motor)  roots  of  the  spinal  nerves.  The  inter- 
vertebral  neural  plates  are  polygonal  pieces  alternating 
with  the  vertebral  neural  plates;  they  are  notched  behind, 
but  at  a  more  dorsal  level  than  are  the  vertebral  neural  plates, 


THE  SKELETON  OF  THE  DOGFISH.   THE  SKULL.   73 

for  the  exit  of  the  dorsal  or  sensory  roots  of  the  spinal 
nerves. 

The  neural  spines  are  small  patches  of  cartilage  filling 
up  the  gaps  between  the  dorsal  ends  of  the  neural  plates. 

The  haemal  arches  (basiventralia)  differ  much  in  the 
trunk  and  tail  portions  of  the  vertebral  column.  In  the 
trunk  portion  the  centra  are  flattened  below,  and  the  two 
halves  of  the  haemal  arch  diverge  from  one  another  as  blunt 
ventri-lateral  processes  to  which  short  cartilaginous  rods, 
the  ribs,  are  attached.  Further  back  at  about  vertebra  37, 
the  two  halves  of  the  haemal  arch  project  downwards  and 
meet  forming  a  complete  arch.  Further  back  still,  towards 
the  hind  end  of  the  tail,  the  haemal  arches  bear  median 
haemal  spines  (ventrispinalia). 

B.     THE  SKULL. 

The  skull  of  the  dogfish  remains  cartilaginous  throughout 
the  life  of  the  animal,  and  has  consequently  a  far  more  simple 
structure  than  have  the  skulls  of  higher  animals,  in  which 
complication  has  been  produced  by  the  development  of  bone. 

The  skull  consists  of  the  following  parts  :  — 

(1)  a  dorsal  portion,  the  cranium,  which  lodges  the  brain, 
and   to  the  sides  of  which  the  capsules  of  the  auditory  and 
olfactory    sense    organs   are   united.     The    cranium    may    be 
compared  to   an  unsegmented  continuation  of  the   vertebral 
column ; 

(2)  a  number  of  ventral  structures,  disconnected  or  only 
loosely  connected   with    the    cranium.      These  together  con- 
stitute  the  visceral   skeleton   forming  the  jaw's  and  sup- 
porting the  gills. 

(1)     THE  CRANIUM. 

The  Cranium  is  an  oblong  box,  with  a  flattened  floor  and 
a  more  irregular  roof.  Its  sides  are  expanded  in  front  owing 


74-         .   THE  VERTEBRATE  SKELETON. 

to  the  olfactory  capsules,  and  behind  owing  to  the  auditory 
capsules,  while  in  the  middle  they  are  deeply  hollowed  to  form 
the  orbits. 

(a)  On  the  dorsal  surface  of  the  cranium  the  following 
points  should  be  noticed.  First  at  the  anterior  end,  the  large 
thin-walled  nasal  or  olfactory  capsules  (fig.  6,  1),  each  of 
which  is  drawn  out  into  a  narrow  cartilaginous  process. 

The  olfactory  capsules  have  no  ventral  walls,  and  are 
separated  from  one  another  by  the  internasal  septum,  which 
is  drawn  out  into  a  third  slender  process.  These  three  pro- 
cesses together  constitute  the  rostrum  (fig.  6,  2). 

Behind  the  olfactory  capsules  comes  a  large,  nearly  circular, 
hole,  the  anterior  fontanelle,  slightly  behind  which  are  the 
two  ophthalmic  foramina.  The  dorsal  and  ventral  bound- 
aries of  the  orbits  are  respectively  formed  by  the  prominent 
supra-orbital  and  sub-orbital  ridges.  Behind  are  the  audi- 
tory capsules  (fig.  6,  8),  each  of  which  is  marked  by  a  pair 
of  prominent  ridges,  converging  towards  the  middle  line  to  a 
pair  of  apertures.  These  apertures  communicate  with  two 
canals,  the  aqueductus  vestibuli,  which  lead  into  the  in- 
ternal ear.  The  two  ridges  lodge  respectively  the  anterior 
and  posterior  vertical  semicircular  canals  of  the  ear. 

(6)  The  principal  structures  to  be  noted  in  a  side  view  of 
the  cranium  are  contained  in  the  orbit  or  eye-cavity.  Near  the 
base  of  the  orbit  at  its  anterior  end  is  seen  the  small  orbito- 
nasal  foramen  (fig.  6,  7),  for  the  passage  of  blood-vessels, 
not  nerves.  Above  it  is  the  large  ophthalmic  foramen 
(fig.  6,  5)  so  prominent  in  a  dorsal  view  of  the  skull ;  through 
it  the  ophthalmic  branches  of  the  fifth  and  seventh  nerves 
pass.  Slightly  further  back  near  the  ventral  surface  is 
the  large  optic  foramen  (fig.  6,  II.)  for  the  passage  of  the 
second  nerve.  Vertically  above  the  optic  foramen,  near  the 
dorsal  surface,  is  the  very  small  foramen  for  the  fourth 
nerve  (fig.  6,  IV.).  Behind  and  a  little  above  the  optic 


THE  SKELETON  OF  THE  DOGFISH.   THE  SKULL.   75 


foramen  is  another  small  aperture,  the  foramen  for  the 
third  nerve.  Behind  and  slightly  below  this  is  the  large 
foramen  for  the  sixth  and  main  branches  of  the  fifth 
and  seventh  nerves  (fig.  6,  V.).  In  front  of  and  slightly 


IX 


FIG.  6.    LATERAL  VIEW  OF  THE  SKULL  OF  A  DOGFISH  (Scyllium 
canicula)    x  f . 


1.  nasal  capsule. 

2.  rostrum. 

3.  interorbital  canal. 

4.  foramen  for  hyoidean  artery. 

5.  foramen  for  the  exit  of  the 

ophthalmic    branches    of 
Vth  and  Vllth  nerves. 

6.  foramen  through  which  the 

external  carotid  leaves  the 
orbit. 

7.  orbitonasal  foramen. 

8.  auditory  capsule. 

9.  foramen  through  which  the 

external  carotid  enters  the 
orbit. 


10.  ethmo -palatine  ligament. 

11.  palato-pterygo-quadrate  bar. 

12.  Meckel's  cartilage. 

13.  hyomandibular. 

14.  cerato-hyal. 

15.  pharyngo-branchial. 

16.  epi-branchial. 

17.  cerato-branchial. 

18.  gill  filaments,  nearly  all  have 

been  cut  off  short  for  the 
sake  of  clearness. 

19.  extra-branchial. 

20.  pre-spiracular  ligament. 

II.  III.  IV.  V.  Va.  Vila,  foramina 
for  passage  of  cranial  nerves. 


below  this  foramen  are  seen  two  other  small  apertures;  the 
more  anterior  and  ventral  of  these  (fig.  6,  4)  is  for  the 
passage  of  a  vessel  connecting  the  efferent  artery  of  the  hyoid 
gill  with  the  internal  carotid  artery  inside  the  skull,  the  more 


76  THE  VERTEBRATE  SKELETON. 

posterior  and  dorsal  is  for  the  interorbital  canal  (fig.  6,  3) 
which  unites  the  two  orbital  sinuses.  Above  and  very  slightly 
in  front  of  the  large  foramen  for  the  sixth  and  main  parts 
of  the  fifth  and  seventh  nerves,  are  two  small  foramina 
(fig.  6,  Va.,  and  Vila.),  through  which  the  ophthalmic 
branches  of  the  fifth  and  seventh  nerves  enter  the 
orbit.  Behind  and  slightly  below  the  large  foramen  just 
mentioned  is  a  small  hole  through  which  the  external  carotid 
enters  the  orbit  (fig.  6,  9). 

Behind  the  orbit  is  the  auditory  capsule.  This  is 
marked  below  by  a  prominent  surface  for  the  articulation 
of  the  hyomandibular,  above  which  is  the  deep  post- 
orbital  groove  for  the  passage  of  a  blood-vessel,  connecting 
the  orbital  and  anterior  cardinal  sinuses. 

(c)  Passing  to  the  posterior  end  of  the  cranium  :  in  the 
centre  is  seen  the  large  foramen  magnum  through  which 
the  brain  and    spinal    cord    communicate.      The  notochord 
enters  the  skull  just  below  this  foramen,  and  on  each  side  of 
the   notochord   is   a   projection,   the  occipital  condyle,  by 
which  the  first  vertebra  articulates  with  the  skull. 

External  to  the  condyles  are  the  prominent  pneumo- 
gastric  foramina  for  the  passage  of  the  tenth  nerves,  and 
further  to  the  sides,  just  beyond  the  posterior  vertical  semi- 
circular canals,  are  a  pair  of  deep  pits  in  which  lie  the 
foramina  for  the  ninth  nerves  (fig.  6,  IX.). 

(d)  The  broad  and  flat  ventral  surface  of  the  cranium  is 
continued  in  front  as  the  inter-nasal  septum  and  terminated 
laterally  by  the  sub-orbital  ridges.     At  a  little  behind  the 
middle  it  is  traversed  by  two  shallow   grooves   along  which 
the  internal  carotid  arteries  run.     At  the  divergent  ends  of 
these  grooves  are  seen  two  small  apertures  through  which  the 
external  carotids  enter  the  orbit  (fig.  6,  9),  and  at  the  point 
where  they  meet  is  a  single  small  aperture  through  which  the 
internal  carotid  enters  the  cranium. 


THE  SKELETON  OF  THE  DOGFISH.     VISCERAL  SKELETON.    77 
(2)     THE  VISCERAL  SKELETON. 

The  Visceral  skeleton  forms  a  series  of  seven  cartilagi- 
nous arches  or  hoops,  surrounding  the  anterior  part  of  the 
alimentary  canal,  and  enclosing  a  wide  but  rather  shallow 
space. 

(a)  The  first  or  mandibular  arch  is  the  largest  of  the 
series,  and  forms  the  upper  and  lower  jaws.  Each  half  of  the 
upper  jaw  or  palato-pterygo-quadrate  bar  is  formed  by  a 
thick  cartilaginous  rod  which  meets  its  fellow  in  the  middle 
line  in  front,  the  two  being  united  by  ligament.  Each  half  is 
connected  to  the  cranium  just  in  front  of  the  orbit  by  the 
ethnic-palatine  ligament  (fig.  6,  10),  and  at  its  hind  end 
articulates  with  one  of  the  halves  of  the  lower  jaw.  Each 
half  of  the  lower  jaw  or  Meckel's  cartilage  (fig.  6,  12)  is 
a  cartilaginous  bar,  wide  behind  but  narrow  in  front,  where 
it  is  united  to  its  fellow  by  a  median  ligament.  Imbedded 
in  the  tissue  external  to  the  upper  jaw  are  a  pair  of 
labial  cartilages,  and  a  similar  but  smaller  pair  are 
imbedded  in  the  tissue  external  to  the  lower  jaw. 

The  jaws  are  developed  from  a  structure  whose  dorsal  and 
ventral  portions  subsequently  become  of  very  different  import- 
ance. The  ventral  portion  forms  both  upper  and  lower  jaws, 
the  former  being  developed  as  an  outgrowth  from  the  latter. 
The  dorsal  portion  forms  only  the  prespiracular  ligament 
(fig.  6,  20),  a  strong  fibrous  band  containing  a  nodule  of 
cartilage,  and  running  from  the  anterior  part  of  the  auditory 
capsule  to  the  point  where  the  jaws  are  connected  with  the 
hyomandibular. 

(6)  The  hyoid  arch  consists  of  a  pair  of  cartilaginous 
rods  which  are  attached  at  their  dorsal  ends  to  the  cranium, 
and  are  united  ventrally  by  a  broad  median  plate  of  cartilage, 
the  basi-hyal.  Each  rod  is  divided  into  a  dorsal  portion, 
the  hyomandibular  and  a  ventral  portion,  the  cerato-hyal. 


78  THE  VERTEBRATE  SKELETON. 

The  hyomandibular  (fig.  6, 13)  is  a  short  stout  rod  of  cartilage 
projecting  outwards,  and  somewhat  backwards  and  downwards 
from  the  cranium,  with  which  it  articulates  behind  the  orbit 
and  below  the  postorbital  groove.  Its  distal  end  articulates 
with  a  rather  long  slender  bar,  the  cerato-hyal  (fig.  6,  14), 
which  is  in  its  turn  attached  to  the  side  of  the  basi-hyal.  The 
basi-hyal  is  a  broad  plate,  rounded  in  front  and  drawn  out 
behind  into  two  processes  to  which  the  two  halves  of  the 
first  branchial  arch  are  attached.  The  posterior  surfaces  of 
both  hyomandibular  and  cerato-hyal  bear  slender  cartilaginous 
processes,  the  gill  rays.  The  hyoid  arch  forms  the  main 
suspensorium  or  means  by  which  the  jaws  are  attached  to 
the  cranium.  This  attachment  is  chiefly  brought  about  by 
a  series  of  short  ligaments  which  connect  the  posterior  ends 
of  both  upper  and  lower  jaws  with  the  hyomandibular,  but 
there  is  also  a  ligament  connecting  the  lower  jaw  with  the 
cerato-hyal.  The  attachment  of  the  jaws  to  the  cranium  is 
also  partially  effected  by  the  prespiracular  and  ethmo-palatine 
ligaments. 

(c)  Each  of  the  five  branchial  arches  is  a  hoop,  in- 
complete above  and  formed  of  four  or  more  pieces  of  cartilage. 
The  most  dorsal  elements,  the  pharyngo-branchials,  are 
flattened,  pointed  plates  whose  free  inner  ends  run  obliquely 
backwards,  and  terminate  below  the  vertebral  column.  They 
are  connected  at  their  outer  ends  with  the  short  broad  epi- 
branchials  (tig.  6,  16)  which  lie  at  the  sides  of  the  pharynx. 
From  the  epi-branchials  arise  the  long  cerato-branchials 
(fig.  6,  17)  which  run  forwards  and  inwards  along  the  ventral 
wall  of  the  pharynx.  The  first  four  cerato-branchials  are 
connected  with  small  rods,  the  hypo-branchials,  which  run 
backwards  to  meet  one  another  in  the  middle  line.  The  last 
two  pairs  of  hypo-branchials  and  the  fifth  cerato-branchials 
are  connected  with  a  broad  median  plate,  the  basi-branchial. 
Along  the  outer  sides  of  the  second,  third  and  fourth  cerato- 


THE    SKELETON   OF   THE    DOGFISH.     MEDIAN    FINS.      79 

branchials  are  found  elongated  curved  rods,  the  extra- 
branchials  (fig.  6,  19).  The  epi- branchials  and  cerato- 
branchials  bear  gill  rays  along  their  posterior  borders. 

C.     THE  SKELETON  OF  THE  MEDIAN  FINS. 

The  dorsal  fins  have  a  skeleton  consisting  of  a  series  of 
short  cartilaginous  rods,  the  basals  or  basalia,  which  slope 
obliquely  backwards.  Their  bases  are  imbedded  in  the 
muscles  of  the  back,  while  their  free  ends  bear  a  number 
of  small  polygonal  cartilaginous  plates,  the  radials  or  radialia. 
Associated  with  this  cartilaginous  skeleton  are  a  number  of 
long  slender  horny  fibres,  the  fin-rays,  which  have  been  already 
referred  to  in  connection  with  the  exoskeleton.  The  skeleton 
of  the  other  median  fins  mainly  consists  of  these  fibres,  the 
cartilaginous  portion  being  reduced  or  absent. 

2.     THE  APPENDICULAR  SKELETON. 

This  includes  the  skeleton  of  the  two  pairs  of  limbs  and  of 
their  respective  girdles. 

THE  PECTORAL  GIRDLE  forms  a  crescent-shaped  hoop  of 
cartilage,  incomplete  above  and  lying  just  behind  the  visceral 
skeleton.  The  midventral  part  of  the  hoop  is  the  thinnest 
portion,  and  is  drawn  out  -in  front  into  a  short  rounded  process 
which  is  cupped  dorsally  and  supports  part  of  the  floor  of  the 
pericardium  (tig.  7,  1).  On  each  side  of  this  flattened  mid- 
ventral  portion  the  arch  becomes  very  thick  and  bears  on  its 
outer  border  a  surface  with  which  the  three  basal  cartilages 
of  the  fin  articulate.  The  dorsal  ends  or  scapular  portions 
of  the  girdle  form  a  pair  of  gradually  tapering  horns. 

THE  PECTORAL  FIN  articulates  with  the  pectoral  girdle  by 
means  of  three  basalia  or  basal  cartilages,  the  pro-pterygium, 
meso-pterygium  and  meta-pterygium.  The  most  anterior 
and  the  smallest  of  these  is  the  pro-pterygium  (fig.  7,  5), 


80 


THE  VERTEBRATE  SKELETON. 


while  the  most  posterior  one,  the  meta-pterygium.  (fig.  7,  3), 
is  much  the  largest.     Along  the  outer  borders  of  the  three 


FIG.  7.     SEMIDORSAL  VIEW  OF  THE  PECTORAL,  GIRDLE  AND  FINS 

OF  A  DOGFISH  (Scyllium  canicula)  x  f . 
The  gaps  between  the  radialia  are  blackened. 


1.  hollow  in  the  midveiitral  part  5. 

of  the  pectoral  girdle  which  6. 

supports  the  pericardium.  7. 

2.  dorsal  (scapular  portion)  of  8. 

pectoral  girdle.  9. 

3.  meta-pterygiuin. 

4.  meso-pterygium. 


pro-pterygium. 
pro-pterygial  radial, 
meso-pterygial  radial, 
meta-pterygial  radial, 
outline  of  the  distal  part  of 

the  fin  which  is  supported 

by  horny  fin-rays. 


basalia  are  arranged  a  series  of  close  set  cartilaginous  pieces, 
the  radialia.  The  pro-pterygium  supports  only  a  single  radial, 
which  is  however  much  larger  than  any  of  the  others.  The 
meso-pterygium  also  supports  only  a  single  radial  which  divides 
distally. 


THE    SKELETON    OF   THE    DOGFISH.      PELVIC  GIRDLE.      81 


long    narrow 


The  meta-pterygium  bears  about  twelve 
radials,  the  first  nine  of  which  are  traversed  by  a  transverse 
joint  at  about  two-  thirds  of  the  way  from  their  origin.  Suc- 
ceeding the  radials  are  a  series  of  small  polygonal  pieces  of 
cartilage  arranged  in  one  or  more  rows  and  attached  to  the  ends 
of  the  radials,  and  finally  the  fin  is  completed  by  the  dermal 
fin-rays. 


FIG.  8.     DORSAL  VIEW  OF  THE  PELVIC  GIEDLE  AND  FINS  OF  A 
MALE  DOGFISH  (Scy Ilium  canicula). 


1.  pelvic  girdle. 

2.  basi-pterygium. 


3.  clasper. 

4.  radialia. 


THE  PELVIC  GIRDLE  is  much  smaller  than  the  pectoral. 
It  is  formed  of  a  stout  nearly  straight  bar  of  cartilage  placed 
transversely  across  the  ventral  region  of  the  body.  The  bar 
has  no  dorsal  or  lateral  extensions,  and  is  terminated  by  short 
blunt  processes.  It  bears  on  its  posterior  surface  a  pair  of 
facets  with  which  the  pelvic  fins  articulate. 

THE  PELVIC  FIN  is  smaller  and  more  simply  constructed 
than  is  the  pectoral.     It  consists  of  a  long,  somewhat  curved 
R.  6 


82  THE  VERTEBRATE  SKELETON. 

rod,  the  basi-pterygium  (fig.  8,  2),  running  directly  backwards 
on  the  inner  side  of  the  fin,  and  articulating  in  front  with  the 
pelvic  girdle.  From  its  outer  side  arise  a  series  of  about 
fourteen  parallel  cartilaginous  radials  which  bear  smaller 
polygonal  pieces.  The  anterior  one  or  two  of  these  radials  may 
articulate  independently  with  the  pelvic  girdle.  In  the  adult 
male  dogfish  the  distal  end  of  the  basi-pterygium  bears  a  stout 
rod  nearly  as  long  as  itself,  and  grooved  on  the  dorsal  surface. 
This  is  the  skeleton  of  the  clasper  (fig.  8,  3). 


CHAPTER    VII. 
THE  SKELETON  OF  THE  CODFISH1.     (Gadus  morrhua.) 

I.  EXOSKELETON. 

The  exoskeleton  includes 

(1)  Scales.     These  are  of  the  type  known  as  cycloid 
and  consist  of  flat  rounded  plates  composed  of  concentrically 
arranged  laminae  of  calcined  matter,  with  the  posterior  margin 
entire.     The  anterior  end  of  each  scale  is  imbedded  in  the  skin 
and  is  overlapped  by  the  preceding  scales. 

(2)  The  teeth.     These  are  small,  pointed,  calcified  struc- 
tures arranged  in  large  groups  on  the  premaxillae,  mandible, 
vomer,  and  superior  and  inferior  pharyngeal  bones. 

(3)  The    fin-rays.      These  are   delicate,  nearly  straight 
bony  rods  which  support  the  fins. 

II.  ENDOSKELETON. 

The  endoskeleton  of  the  Codfish,  though  partially  carti- 
laginous, is  mainly  ossified. 

It  is  divisible  into  an  axial  portion,  including  the  skull, 
vertebral  column,  ribs,  and  skeleton  of  the  median  fins,  and 
an  appendicular  portion,  including  the  skeleton  of  the 
paired  fins  and  their  girdles. 

1.     THE  AXIAL  SKELETON. 
A.     THE  VERTEBRAL  COLUMN. 

This  consists  of  a  series  of  some  fifty-two  vertebrae,  all  com- 
pletely ossified. 

1  See  T.  J.  Parker's  Zootomy,  London,  1884,  p.  86. 

0—2 


84  THE  VERTEBRATE  SKELETON. 

It  is  divisible  into  two  regions  only,  viz.  the  trunk  region, 
the  vertebrae  of  which  bear  movable  ribs,  and  the  caudal  or 
tail  region,  the  vertebrae  of  which  do  not  bear  movable  ribs. 

Trunk  vertebrae. 

These  are  seventeen  in  number;  the  ninth  may  be  de- 
scribed as  typical  of  them  all.  It  consists  of  a  short  deeply 
biconcave  centrum  whose  two  cavities  communicate  by  a 
narrow  central  canal.  From  the  dorsal  surface  of  the  anterior 
half  of  the  centrum  arise  two  strong  plates,  the  dorsal  or 
neural  processes,  which  are  directed  obliquely  backwards 
and  meet  forming  the  dorsal  or  neural  arch.  This  is  pro- 
duced into  a  long  backwardly  -  directed  dorsal  or  neural 
spine. 

From  the  lower  part  of  the  anterior  edge  of  each  neural 
arch  arise  a  pair  of  blunt  triangular  projections  which  over- 
hang the  posterior  half  of  the  preceding  centrum,  and  bear  a 
pair  of  flattened  surfaces  which  correspond  to  the  anterior 
or  pre-zygapophyses  of  most  vertebrae,  they  differ  however 
from  ordinary  pre-zygapophyses  in  the  fact  that  they  look 
downwards  and  outwards.  From  the  posterior  end  of  the 
centrum  arise  a  pair  of  short  blunt  processes  each  of  which 
bears  an  upwardly-  and  inwardly-directed  articulating  surface 
corresponding  to  a  post-zygapophysis. 

The  two  halves  of  the  ventral  arch  form  a  pair  of  large 
ventri-lateral  processes  which  arise  from  the  anterior  half 
of  the  centrum  and  pass  outwards  and  slightly  backwards  and 
downwards. 

Behind  these  there  arises  on  each  vertebra  a  second  out- 
growth which  is  small  and  flattened,  and  like  the  ventri- 
lateral  process  serves  to  protect  the  air-bladder.  The  surface 
of  the  centrum  is  marked  by  more  or  less  wedge-shaped  de- 
pressions, one  in  the  mid-dorsal  line,  and  two  on  the  ventral 
surface  immediately  mesiad  to  the  bases  of  the  ventri-lateral 
process.  There  are  also  a  number  of  smaller  depressions. 


THE  SKELETON  OF  THE  CODFISH.   VERTEBRAE.   85 

The  space  between  one  centrum  and  the  next  is  in  the  fresh 
skeleton  filled  up  by  the  gelatinous  remains  of  the  notochord. 

The  first  few  vertebrae  differ  from  the  others  in  having 
very  short  centra  and  no  ventri-lateral  processes. 

The  first  vertebra  comes  into  very  close  relation  to  the 
posterior  part  of  the  skull,  articulating  with  the  exoccipitals. 
In  the  next  few  vertebrae  the  centra  gradually  lengthen, 
and  at  the  fourth  or  fifth  vertebra  the  ventri-lateral  pro- 
cesses appear  and  gradually  increase  in  size  as  followed  back. 
They  likewise  gradually  come  to  arise  at  a  lower  level  on  the 
centrum,  and  also  become  more  and  more  downwardly  directed, 
till  at  the  last  trunk  vertebra  they  nearly  meet. 

The  neural  spines  of  the  anterior  trunk  vertebrae  are 
much  longer  than  those  of  the  posterior  ones,  that  of  the  first 
vertebra  being  the  largest  and  longest  of  all,  and  articulating 
with  the  skull.  The  spinal  nerves  pass  out  through  wide 
notches  or  spaces  between  the  successive  neural  arches. 

Caudal  vertebrae. 

The  caudal  vertebrae  are  about  thirty -five  in  number, 
each  consists  of  a  centrum  with  a  slender  backwardly-directed 
dorsal  or  neural  arch,  similar  to  those  of  the  posterior  trunk 
vertebrae.  The  two  halves  of  the  ventral  or  haemal  arch 
however  do  not  form  outwardly-directed  ventri-lateral  pro- 
cesses, but  arise  on  the  ventral  surface  of  the  centrum,  and 
passing  downwards  meet  and  enclose  a  space;  they  thus 
form  a  complete  canal,  and  are  prolonged  into  a  backwardly- 
directed  ventral  or  haemal  spine.  The  anterior  haemal 
arches  are  much  larger  than  the  corresponding  neural  arches, 
but  when  followed  back  they  gradually  decrease  in  size,  till  at 
about  the  twenty-fourth  caudal  vertebra  they  are  nearly  as 
small  as  the  neural  arches.  The  last  caudal  vertebra  is  suc- 
ceeded by  a  much  flattened  hypural  bone  or  urostyle,  which 
together  with  the  posterior  neural  and  haemal  spines  supports 
the  tail-fin. 


86  THE  VERTEBRATE  SKELETON. 

B.  THE  RIBS. 

The  ribs  are  slender,  more  or  less  cylindrical  bones  at- 
tached to  the  postero-dorsal  faces  of  the  ventri-lateral  pro- 
cesses of  all  the  trunk  vertebrae  except  the  first  and  second. 
The  earlier  ones  are  thicker  and  more  curved  ;  the  later  ones 
thinner  and  more  nearly  straight.  The  ribs  are  homologous 
with  the  distal  parts  of  the  haemal  arches  of  the  caudal 
vertebrae. 

Associated  with  the  ribs  are  a  second  series  of  rib-like 
bones,  the  intermuscular  bones.  These  are  slender,  curved 
bones  which  arise  from  the  ribs  or  from  the  ventri-lateral 
processes  at  a  distance  of  about  an  inch  from  the  centra,  and 
curve  upwards,  outwards  and  backwards.  In  the  anterior 
region  where  the  ventri-lateral  processes  are  short  they  arise 
from  the  ribs,  further  back  they  arise  from  the  ventri-lateral 
processes. 

C.  THE  UNPAIRED  OR  MEDIAN  FINS. 

These  are  six  in  number,  three  being  dorsal,  one  caudal 
and  two  anal. 

The  dorsal  and  anal  fins  each  consist  of  two  sets  of 
structures,  the  fin-rays  and  the  interspinous  bones.  Each 
fin-ray  forms  a  delicate,  nearly  straight,  bony  rod  which 
becomes  thickened  and  bifurcated  at  its  proximal  or  vertebral 
end,  while  distally  it  is  transversely  jointed  and  flexible, 
frequently  also  becoming  more  or  less  flattened. 

The  first  dorsal  fin  has  thirteen  rays,  the  second,  sixteen  to 
nineteen,  the  third,  seventeen  to  nineteen.  The  first  anal  fin 
has  about  twenty-two,  the  second  anal  fourteen.  In  each 
fin  the  posterior  rays  rapidly  decrease  in  size  when  followed 
back. 

The  interspinous  bones  of  the  dorsal  and  anal  fins 
alternate  with  the  neural  and  haemal  spines  respectively,  and 
form  short,  forwarclly-projecting  bones,  each  attached  proxi- 
mally  to  the  base  of  the  corresponding  fin-ray. 


THE  SKELETON  OF  THE  CODFISH.   CAUDAL  FIN.   87 

The  caudal  fin  consists  of  a  series  of  about  forty-three 
rays  which  radiate  from  the  posterior  end  of  the  vertebral 
column,  being  connected  with  the  urostyle  or  hypural  bone, 
and  with  the  posterior  neural  and  haemal  spines  without  the 
intervention  of  interspinous  bones.  Like  the  other  fin-rays 
those  forming  the  caudal  fin  are  transversely  jointed,  and  are 
widened  and  frayed  out  distally. 

The  tail -fin  in  the  Cod  is  homocercal,  i.e.  it  appears 
to  be  symmetrically  developed  round  the  posterior  end  of 
the  vertebral  column,  though  in  reality  a  much  greater  pro- 
portion is  attached  below  the  end  of  the  vertebral  column  than 
above  it.  It  is  a  masked  heterocercal  tail. 

THE  SKULL. 

Owing  to  the  fact  that  very  little  cartilage  remains  in 
the  skull  of  the  adult  Codfish,  its  relation  to  the  completely 
cartilaginous  skull  of  the  Dogfish  is  not  easily  seen.  Before 
describing  it  therefore,  the  skull  of  the  Salmon  will  be  de- 
scribed, as  it  forms  an  intermediate  type. 

THE   SKULL   OF   THE   SALMON1. 

The  Salmon's  skull  consists  of  (1)  the  chondrocranium, 
which  remains  partly  cartilaginous  and  is  partly  converted 
into  cartilage  bone,  especially  in  the  occipital  region,  (2)  a 
large  series  of  plate-like  membrane  bones. 

THE  CHONDROCRANIUM. 

This  is  an  elongated  structure,  wide  behind  owing  to  the 
fusion  of  the  large  auditory  capsules  with  the  cranium,  and 
elongated  and  tapering  considerably  in  front ;  in  the  middle 
it  is  much  contracted  by  the  large  orbital  cavities. 

DORSAL  SURFACE  OF  THE  CRANIUM. 

In  the  centre  of  the  posterior  end  of  the  dorsal  surface 
is  the  supra- occipital  (fig.  9,  A,  1)  with  a  prominent  posterior 

1  See  W.  K.  Parker  and  G.  T.  Bettany,  The  Morphology  of  the  Skull, 
London,  1877,  chap.  3. 


88 


THE  VERTEBRATE  SKELETON. 


B 


,8 


18 


FlG.    9.      A.    DORSAL  AND   B.    VENTRAL  VIEW  OF    THE    CRANIUM   OF   A    SALMON 

(Salmo  solar)  from  which  most  of  the  membrane  bones  have  been 
removed  (after  PARKER).     Cartilage  is  dotted. 


1.  supra-occipital. 

2.  epi-otic. 

3.  pterotic. 

4.  sphenotic. 

5.  frontal. 

6.  median  ethmoid. 

7.  parietal. 

8.  lateral  ethmoid. 

9.  para  sphenoid. 

10.  vomer. 

11.  exoccipital. 


12.  opisthotic. 

13.  alisphenoid. 

14.  orbitosphenoid. 

16.  foramen   for  passage  of  an 

artery. 

17.  pro-otic. 

18.  articular    surface    for    hyo- 

mandibular. 

II.  VII.  IX.  X.  foramina  for  the 
passage  of  cranial  nerves. 


THE  SKULL  OF  THE  SALMON.  89 

ridge.  It  is  separated  by  two  tracts  of  unossified  cartilage 
from  the  large  series  of  bones  connected  with  the  auditory 
organ.  The  first  of  these  is  the  epi-otic  (fig.  9,  2),  which  is 
separated  by  only  a  narrow  tract  of  cartilage  from  the  supra- 
occipital,  and  is  continuous  laterally  with  the  large  pterotic 
(fig.  9,  A,  3)  which  overlaps  in  front  a  smaller  bone,  the 
sphenotic  (fig.  9,  4).  Both  epi-otic  and  pterotic  are  drawn  out 
into  rather  prominent  backwardly-projecting  processes. 

The  greater  part  of  the  remainder  of  the  dorsal  surface 
is  formed  of  unossified  cartilage  which  is  pierced  by  three 
large  vacuities  or  fontanelles.  The  anterior  fontanelle  is 
unpaired,  and  lies  far  forward  near  the  anterior  end  of  the 
long  cartilaginous  snout,  the  two  larger  posterior  ones  lie 
just  in  front  of  the  supra-occipital  and  lead  into  the  cranial 
cavity.  In  front  of  the  orbit  the  skull  widens  again,  and 
is  marked  by  two  considerable  lateral  ethmoid  (fig.  9,  8) 
ossifications.  In  front  of  these  are  a  pair  of  deep  pits,  the 
nasal  fossae,  at  the  base  of  which  are  a  pair  of  foramina 
through  which  the  olfactory  nerves  pass  out ;  they  communicate 
with  a  space,  the  middle  narial  cavity,  seen  in  a  longitu- 
dinal section  of  the  skull. 

The  long  cartilaginous  snout  is  more  or  less  bifid  in  front, 
especially  in  the  male  (fig.  9). 

POSTERIOR  END  OF  THE  CRANIUM. 

The  foramen  magnum  forms  a  large  round  hole  leading 
into  the  cranial  cavity,  and  is  bounded  laterally  by  the  two 
exoccipitals  and  below  by  them,  and  to  a  very  slight  extent 
by  the  basi-occipital,  the  three  bones  together  forming  a 
concave  occipital  condyle  by  which  the  vertebral  column 
articulates  with  the  skull. 

The  exoccipitals  are  connected  laterally  with  a  fourth 
pair  of  auditory  bones,  the  opisthotics,  and  just  meet  the 
epi-otics  dorsolaterally,  while  dorsally  they  are  separated  by  a 
wide  tract  of  unossified  cartilage  from  the  supra-occipital. 

The  opisthotics  are  connected  laterally  with  the  pterotics. 


90 


THE  VERTEBRATE  SKELETON. 


SIDE  OF  THE  CRANIUM. 

At  the  posterior  end  is  seen  the  basi-occipital  in  contact 
above  with  the  exoccipital,  which  is  pierced  by  a  prominent 

1 


10 


17 


FIG.  10.     LATERAL  VIEW  OF 
salar)   (after  PARKER). 
Cartilage  is  dotted. 
1.     supra-occipital, 
epi-otic. 
pterotic. 
opisthotic. 
exoccipital. 
basi-occipital. 
parasphenoid. 
sphenotic. 
alisphenoid. 
orbitosphenoid. 
lateral-  or  ectethmoid. 


9. 
10. 
11. 


THE    CHONDROCRANIUM    OF   A    SALMON    (SdlmO 

A  few  membrane   bones   are   also   shown. 

12.     olfactory  pit ;    the  vomerine 
teeth  are  seen  just  below. 

14.  pro-otic. 

15.  basisphenoid. 

16.  foramen  for  the  passage  of 

an  artery. 

17.  anterior  fontanelle. 

18.  posterior  fontanelle. 

I.  II.  V.  VII.  IX.  X.  foramina 
for  the  passage  of  cranial  nerves. 


foramen  for  the  exit  of  the  tenth  nerve.     In  front  of  this  lies 
a  small  foramen,  sometimes  double,  for  the  ninth  nerve. 

In  front  of  the  exoccipital  is  the  large  pro-otic  pierced 
by  two  prominent  foramina.  Through  the  more  dorsal  of  these 
(fig.  10,  VII.)  the  facial  nerve  passes  out,  while  the  more 
ventral  (fig.  10,  16)  is  for  the  passage  of  an  artery.  Dorsal  to 
the  exoccipital  are  the  opisthotic  and  pterotic,  and  dorsal  to 


THE  SKULL  OF  THE  SALMON.  91 

the  pro-otic  is  the  sphenotic.  The  pterotic  is  marked  by  a 
prominent  groove  often  lined  by  cartilage,  which  is  continued 
forwards  along  a  tract  of  cartilage  between  the  pro-otic  and 
sphenotic.  With  this  groove  the  hyomandibular  articulates. 

There  are  considerable  ossifications  in  the  sphenoidal  region 
of  the  side  of  the  cranium.  The  anterior  boundary  of  the  pos- 
terior fontanelle  is  formed  by  the  large  alisphenoid,  which 
is  continuous  behind  with  the  pro-otic  and  sphenotic,  and 
below  with  a  slender  basisphenoid.  Both  in  front  of  and 
behind  the  basisphenoid  there  are  considerable  vacuities  in  the 
walls  of  the  cranium ;  through  the  posterior  of  these  openings 
(fig.  10,  V.)  the  main  part  of  the  trigeminal  nerve  passes  out, 
and  through  the  anterior  one,  the  optic  (fig.  10,  II.).  The 
alisphenoid  is  continuous  in  front  with  the  orbitosphenoid 
(fig.  10,  10),  which  is  pierced  by  the  foramen  for  the  exit  of 
the  first  nerve  (fig.  10,  I.),  and  in  front  of  the  orbitosphenoid 
there  is  a  large  vacuity.  The  lateral  ethmoid  is  seen  in  the 
side  view  as  well  as  in  the  dorsal  view.  Further  forwards  are 
seen  the  olfactory  pits,  and  the  long  cartilaginous  snout. 

A  ventral  view  of  the  cartilaginous  cranium  shows  much 
the  same  points  as  the  side  view.  The  basisphenoid  appears 
on  the  surface  immediately  in  front  of  the  basi-occipital. 

THE  SKULL  WITH  MEMBRANE  BONES. 

The  dorsal  surface.  The  greater  part  of  the  dorsal 
surface  in  front  of  the  supra-occipital  is  overlaid  by  a  pair 
of  large  rough  f rentals  (figs.  9,  A,  5,  and  10,  5).  They  cover 
the  posterior  fontanelles  and  stretch  over  from  the  sphenotic 
to  the  lateral  ethmoid,  forming  a  roof  for  the  orbit.  They 
meet  in  the  middle  line  behind,  but  in  front  are  separated 
by  a  narrow  tract  of  unossified  cartilage,  and  are  overlapped 
by  the  median  ethmoid  (figs.  9,  A>  6,  and  11,  6).  At  the  sides 
of  the  supra  occipital  behind  the  f  rentals  are  a  pair  of  small 
parietals  (tigs.  9,  A,  7,  and  11,  7). 

In   a  ventral  view   the   cranium  is  seen  to    be  chiefly 


92 


THE  VERTEBRATE  SKELETON. 


FIG.  11.     LATERAL  VIEW  OF  THE  SKULL  or  A  SALMON  (Salmo  solar) 
(after  PARKER).    Cartilage  is  dotted. 


1.  supra-occipital. 

2.  epi-otic. 

3.  pterotic. 

4.  sphenotic. 

5.  frontal. 

6.  median  ethmoid. 

7.  parietal. 

8.  nasal. 

9.  lachrymal. 

10.  sub-orbital. 

11.  supra-orbital. 

12.  cartilaginous  sclerotic. 

13.  ossification  in  sclerotic. 

14.  meso-pterygoid. 

15.  meta-pterygoid. 

16.  palatine. 

17.  jugal. 

18.  quadrate. 


19.  maxilla. 

20.  premaxilla. 

21.  articular. 

22.  angular. 

23.  dentary. 

24.  hyomandibular. 

25.  symplectic. 

26.  epi-hyal. 

27.  cerato-hyal. 

28.  hypo-hyal. 

29.  glosso-hyal. 

30.  opercular. 

31.  sub-opercular. 

32.  infra- opercular. 

33.  pre-opercular. 

34.  supratemporal. 

35.  branchiostegal  rays. 

36.  basi-branchiostegal. 


THE  SKULL  OF  THE  SALMON.  93 

covered  by  two  large  membrane  bones,  the  parasphenoid 
(fig.  9,  B,  9)  behind,  the  vomer  in  front.  A  view  of  the 
posterior  end  differs  from  that  of  the  cartilaginous  cranium 
only  in  the  fact  that  the  end  of  the  parasphenoid  appears 
lying  ventral  to  the  basi-occipital. 

The  lateral  view  differs  very  markedly  from  that  of  the 
cartilaginous  cranium,  there  being  a  great  development  of 
membrane  bone  in  connection  with  the  jaws  and  branchial 
apparatus.  Lying  dorsally  are  seen  the  median  ethmoid,  frontal, 
parietal,  and  supra-occipital  as  before.  Lying  external  to 
the  middle  of  the  median  ethmoid  is  seen  the  small  nasal 
(fig.  11,  8),  and  below  the  hinder  part  is  the  lachrymal  The 
lachrymal  (fig.  11,  9)  forms  the  first  of  a  series  of  seven  small 
bones  which  surround  the  orbit  forming  the  orbital  ring. 
Of  these  the  one  lying  immediately  in  the  mid  ventral  line  of 
the  orbit  is  the  sub-orbital,  while  the  one  lying  in  the  mid- 
dorsal  line  and  attached  to  the  frontal  is  the  supra-orbital 
(fig.  11,  11).  The  orbit  has  a  cartilaginous  sclerotic  in  which 
are  two  small  ossifications  (fig.  11,  13)  laterally  placed. 

BONES    OF    THE    UPPER    JAW. 

The  palato-pterygo-quadrate  bar  is  in  a  very  different 
condition  from  that  of  the  dogfish,  it  is  partially  cartilaginous, 
partially  converted  into  cartilage  bone,  partially  overlapped  by 
membrane  bone.  It  is  narrow  in  front  but  becomes  much 
broader  and  deeper  when  followed  back.  Its  anterior  end  forms 
the  palatine  which  bears  teeth,  and  in  front  is  completely 
ossified,  while  behind  the  cartilage  is  only  sheathed  by  bone. 

Just  behind  the  palatine  the  outer  part  of  the  cartilage  is 
ossified,  forming  two  small  bones,  the  pterygoid  and  meso- 
pterygoid,  while  behind  them  is  a  larger,  somewhat  square 
bone,  the  meta-pterygoid  (fig.  11,  15). 

Below  the  meta-pterygoid  is  a  tract  of  unossified  carti- 
lage, and  then  comes  the  quadrate  (fig.  11,  18). 


94  THE  VERTEBRATE  SKELETON. 

The  lower  angle  of  the  quadrate  bears  a  cartilaginous  con- 
dyle  with  which  the  mandible  articulates.  In  front  of  the 
palatine  the  cartilaginous  snout  is  overlapped  by  three  mem- 
brane bones,  the  jugal,  maxilla  and  preinaxilla. 

The  premaxilla  (fig.  11,  20),  the  largest  of  these,  overlaps 
the  maxilla  behind  ;  both  bones  bear  teeth.  The  jugal  (fig.  11, 
17)  lies  above  the  maxilla  and  overlaps  it  in  front. 

THE  LOWER  JAW. 

The  lower  jaw  is  a  strong  bar  and  is  like  the  upper  jaw, 
partly  cartilaginous,  forming  Meckel's  cartilage,  partly  ossi- 
fied, and  sheathed  to  a  considerable  extent  in  membrane  bone. 

The  outer  side  and  posterior  end  is  ossified,  forming  the 
large  articular  (fig.  11,  21),  but  the  condyle  is  cartilaginous 
and  the  anterior  part  of  the  articular  forms  merely  a  splint  on 
the  outer  side  of  Meckel's  cartilage,  which  extends  beyond  it 
for  a  considerable  distance.  The  angle  of  the  jaw  just  below 
the  condyle  is  formed  by  a  small  angular  (fig.  11,  22),  and  the 
anterior  two-thirds  of  the  jaw  is  sheathed  in  the  large  tooth- 
bearing  dentary  (fig.  11,  23). , 

THE  HYOID  ARCH. 

The  hyoid  arch  has  a  number  of  ossifications  in  it  and  is 
closely  connected  with  the  mandibular  arch. 

The  hyomandibular  (fig.  11,  24)  is  a  large  bone  which 
articulates  with  a  shallow  groove  lined  by  cartilage  and  formed 
partly  in  the  pterotic,  partly  in  front  of  it.  The  hyomandibular 
is  overlapped  in  front  by  the  meta-pterygoid,  while  below  it 
tapers  and  is  succeeded  by  a  small  area  of  unossified  cartilage 
followed  by  the  forwardly-directed  symplectic  which  fits 
into  a  groove  in  the  quadrate. 

The  unossified  tract  between  the  hyomandibular  and  sym- 
plectic is  continuous  in  front  with  a  strong  bar,  which  remains 
partly  cartilaginous  and  is  partly  converted  into  cartilage 
bone.  The  proximal  part  is  ossified,  forming  the  epi-hyal,  the 


THE   SKULL    OF   THE   SALMON. 

middle  part  forms  the  cerato-hyal  (fig.  11,  27),  in  front  of 
which  is  the  small  hypo-hyal.  The  hyoid  arches  of  the  two 
sides  are  united  by  the  large  tooth-bearing  glosso-hyal  (fig.  11, 
29).  Attached  to  the  lower  surface  of  the  hyoid  arch  are  a  series 
of  twelve  flat  branckiostegal  rays  (fig.  11,  35).  Each  overlaps 
the  one  in  front  of  it,  the  posterior  one  being  the  largest.  The 
branchiostegal  rays  of  the  two  sides  are  united  in  front  by  an 
unpaired  membrane  bone,  the  basi-branchiosteyal  (fig.  11,  36). 

Opercular  bones.  Behind  the  hyomandibular  there  is  a 
large  bony  plate,  the  operculum,  formed  of  four  large  mem- 
brane bones.  The  anterior  of  these,  the  pre-opercular  (fig.  11, 
33),  is  crescentic  in  shape,  and  with  its  upper  end  a  small 
supra-temporal  (fig.  11,  34)  is  connected. 

Behind  the  upper  part  of  the  pre-opercular  is  the  largest  of 
the  opercular  bones,  the  opercular  proper.  Its  lower  edge 
overlaps  the  sub-opercular,  and  both  opercular  and  sub- 
opercular  are  overlapped  by  the  infra- opercular  (fig.  11,  32) 
in  front.  The  infra -opercular  is  in  its  turn  overlapped  by 
the  pre-opercular. 

BRANCHIAL  ARCHES. 

There  are  five  branchial  arches,  the  first  four  of  which 
bear  gill  rays.  Each  of  the  first  three  consists  of  a  shorter 
upper  portion  directed  obliquely  backwards  and  outwards, 
and  a  longer  lower  portion  forming  a  right  angle  with  the 
upper  and  directed  obliquely  forwards  and  inwards.  The 
greater  part  of  each  arch  is  ossified. 

The  upper  part  of  either  of  the  first  two  consists  of  a  short 
tapering  pharyngo-branchial  directed  inwards,  and  of  a 
long  epi-branchial  tipped  with  cartilage  at  both  ends.  The 
junction  of  the  upper  and  lower  parts  is  formed  by  a  carti- 
laginous hinge-joint  between  the  epi-branchial  and  cerato- 
branchial.  The  cerato-branchial  is  a  long  bony  rod  sepa- 
rated by  a  short  area  of  cartilage  from  the  hypo -branchial, 
which  is  succeeded  by  the  basi-branchial  meeting  its  fellow 


96  THE  VEHTEBRATE  SKELETON. 

in  the  middle  line.  The  fourth  arch  has  a  short  epi-branchial 
and  no  ossified  pharyn go-branchial,  while  the  fifth  is  reduced 
to  little  more  than  the  cerato-branchial,  which  bears  a  few 
teeth  on  its  inner  edge.  All  the  branchial  arches  have  pro- 
jecting from  their  surfaces  a  number  of  little  processes  which 
act  as  strainers.  The  first  and  fourth  arches  have  one  series 
of  these,  the  second  and  third  have  two. 

THE  SKULL  OF  THE  CODFISH1. 

A  full  description  having  been  already  given  of  the  Salmon's 
skull,  that  of  the  Codfish  will  be  described  in  a  briefer  manner. 
The  skull  is  very  fully  ossified,  and  the  great  number  of  plate- 
like  bones  render  it  a  very  complicated  structure. 

THE  CRANIUM. 

At  the  posterior  end  of  the  dorsal  surface  is  the  large 
supra-occipital,  which  is  drawn  out  behind  into  the  large 
blade-like  occipital  spine.  On  each  side  of  the  supra-occi- 
pital are  the  small  irregular  parietals,  while  in  front  of  it  the 
roof  of  the  skull  is  mainly  formed  by  the  very  large  unpaired 
frontal. 

A  complicated  series  of  bones  are  developed  in  connection 
with  the  auditory  capsule,  which  forms  a  large  projecting 
mass  united  with  the  side  of  the  cranium  and  drawn  out  be- 
hind into  a  pair  of  strong  processes,  the  epi-otic  and  parotic 
processes.  Both  these  processes  are  connected  behind  with  a 
large  Y-shaped  bone,  the  post-temporal  (fig.  13,  1),  which  will 
be  described  when  dealing  with  the  pectoral  girdle.  The  epi- 
otic  process  is  formed  by  the  epi-otic,  which  is  continuous  in 
front  with  the  parietal.  The  parotic  process  is  formed  by 
two  larger  bones,  a  more  dorsal  one,  the  pterotic,  and  a  more 
ventral  and  internal  one,  the  opisthotic,  which  is  continuous 
in  front  with  the  large  pro-otic.  Intervening  between  the 

1  T.  J.  Parker,  Zootomy,  London,  1884,  p.  91. 


THE  SKELETON  OF  THE  CODFISH.   THE  SKULL.   97 

pterotic  and  frontal  is  another  rather  large  bone,  the  sphenotic, 
this  articulates  below  with  the  pro-otic.  The  pterotic  and 
sphenotic  together  give  rise  to  a  large  concave  surface  by 
which  the  hyomandibular  articulates  with  the  cranium. 
Several  of  the  cranial  nerves  pass  out  through  the  bones  of 
the  auditory  capsule.  The  ninth  leaves  by  a  foramen  near 
the  posterior  border  of  the  opisthotic,  the  fifth  and  seventh  by 
a  notch  in  the  anterior  border  of  the  pro-otic. 

A  number  of  bones  are  likewise  developed  in  connection 
with  the  orbit  forming  the  orbital  ring.  Of  these  the  most 
anterior,  the  lachrymal,  is  much  the  largest,  the  others  are 
five  to  seven  in  number,  the  most  ventral  being  the  suborbital. 
The  sclerotic  coat  of  the  eye  is  cartilaginous. 

Two  pairs  of  bones  and  one  unpaired  bone  are  developed  in 
connection  with  the  olfactory  capsules,  of  these,  the  nasals 
are  narrow  bones  lying  next  the  lachrymals,  but  nearer  the 
middle  line ;  they  overlap  the  second  pair  of  bones,  the  ir- 
regular lateral  ethmoids.  These  meet  one  another  in  the 
middle  line,  and  are  overlapped  behind  by  the  frontal.  They 
articulate  laterally  with  the  lachrymal  and  palatine,  and  ven- 
trally  with  the  parasphenoid. 

In  a  posterior  view  the  foramen  magnum  and  the  four 
bones  which  surround  it  and  together  form  the  occipital  seg- 
ment are  well  seen.  On  the  ventral  side  is  the  basi-occipital, 
terminated  posteriorly  by  a  slightly  concave  surface  which 
articulates  with  the  centrum  of  the  first  vertebra.  The  sides 
of  the  foramen  magnum  are  formed  by  the  exoccipitals,  a 
pair  of  very  irregular  bones,  pierced  by  a  pair  of  prominent 
foramina  for  the  exit  of  the  tenth  nerves.  The  exoccipitals 
also  bear  a  pair  of  surfaces  for  articulation  with  corresponding 
ones  on  the  neural  arch  of  the  first  vertebra.  The  most  dorsal 
of  the  four  bones  is  the  supra- occipital. 

On  the  ventral  surface  of  the  cranium  in  front  of  the  basi- 
occipital  is  seen  the  parasphenoid,  a  very  long  narrow  bone 
which  underlies  the  greater  part  of  the  cranium.     Behind,  it 
R.  7 


98  THE  VERTEBRATE  SKELETON. 

articulates  dorsally  with  the  basi-occipital  and  dorsolaterally 
with  the  pro-otics  and  opisthotics,  in  front  it  articulates 
dorsally  with  the  lateral  ethmoid  and  ventrally  with  the 
vomer.  At  the  sides  of  the  parasphenoid  are  the  small  ali- 
sphenoids  articulating  above  with  the  postf rentals,  in  front 
with  the  frontals,  and  behind  with  the  pro-otics. 

The  vomer  is  an  unpaired  bone  lying  immediately  in  front 
of  the  parasphenoid.  In  front  it  terminates  with  a  thickened 
curved  margin  bearing  several  rows  of  small  teeth ;  behind 
it  tapers  out  into  a  long  process  which  underlies  the  anterior 
part  of  the  parasphenoid.  Immediately  dorsal  to  the  vomer 
is  another  median  bone,  the  median  ethmoid]  this  is  truncated 
in  front  and  tapers  out  behind  into  a  process  which  fits  into  a 
groove  on  the  ventral  side  of  the  frontal. 

BONES    IN    CONNECTION    WITH    THE    UPPER    JAW. 

These  bear  a  close  resemblance  to  those  of  the  Salmon. 
The  most  anterior  bone  is  the  premaxilla,  a  thick  curved  bone 
meeting  its  fellow  in  the  middle  line.  The  point  of  junction 
of  the  two  is  drawn  out  into  a  short  process,  and  the  oral 
surface  is  thickly  covered  with  small  teeth.  The  dorsal  ends 
of  the  premaxillae  are  seen  in  the  fresh  skull  to  meet  a  large 
patch  of  cartilage.  Behind  the  premaxilla  is  the  maxilla,  a 
long  rod-like  toothless  bone,  somewhat  expanded  at  the  upper 
end  where  it  articulates  with  the  premaxilla  and  vomer. 

Articulating  in  front  with  the  anterior  end  of  the  maxilla 
and  with  the  lateral  ethmoid  is  a  very  irregular  bone,  the 
palatine  (fig.  12,  1);  it  articulates  behind  with  two  flat 
bones,  the  pterygoid  and  meso-pterygoid.  The  ptery- 
goid  is  united  behind  with  two  more  bones,  the  quadrate 
(fig.  12,  4)  and  meta-pterygoid.  The  quadrate  is  a  rather 
stout  irregular  bone,  bearing  on  its  lower  surface  a  promi- 
nent saddle-shaped  articulating  surface  for  the  mandible. 
The  palatine,  pterygoid  and  quadrate  bones  are  the  ossified 


THE    SKELETON    OF   THE    CODFISH.      UPPER   JAW.        99 

representatives    of    the    palato-ptery  go-quad  rate    bar    of   the 
Dogfish. 


FIG.  12.     MANDIBULAR  AND  HYOID  ARCHKS  OF  A  COD  (Gadus 


morrhua)  x  £  (Brit.  Mus.). 


1.  palatine. 

2.  meso-pterygoid. 

3.  pterygoid. 

4.  quadrate. 

5.  symplectic. 

6.  meta-pterygoid. 

7.  hyomandibular. 

8.  angular. 


9.  articular. 

10.  dentary. 

11.  inter- hyal. 

12.  epi-hyal. 

13.  cerato-hyal. 

14.  hypo-hyal. 

15.  uro-hyal. 

16.  branchiostegal  rays. 


The  quadrate  is  united  behind  with  the  symplectic 
(fig.  12,  5),  and  the  meta-pterygoid  with  the  symplectic  and 
hyomandibular,  both  of  which  bones  will  be  described  im- 
mediately in  connection  with  the  hyoid  arch. 

7—2 


100          THE  VERTEBRATE  SKELETON. 

THE  LOWER  JAW. 

The  lower  jaw  or  mandible  like  that  of  the  Salmon  is 
partly  cartilaginous,  forming  Meckel's  cartilage,  partly 
formed  of  cartilage  bone,  partly  of  membrane  bone.  Meckel's 
cartilage  is  of  course  not  seen  in  the  dried  skull. 

The  lower  jaw  includes  one  cartilage  bone,  the  articular 
(fig.  12,  9),  this  is  a  large  bone  connected  by  a  saddle- 
shaped  surface  with  the  quadrate.  Meckel's  cartilage  lies  in 
a  groove  on  its  under  surface,  and  projects  beyond  it  in  front. 
The  angular  is  a  small  thick  bone  united  to  the  lower  surface 
of  the  articular  at  its  posterior  end.  The  dentary  (fig.  12,  10) 
is  a  large  tooth-bearing  bone  meeting  its  fellow  in  the  middle 
line  in  front,  while  the  articular  fits  into  a  deep  notch  at  its 
posterior  end. 

THE  HYOID  ARCH. 

The  hyomandibular  (fig.  12,  7)  is  a  large  irregular  bone, 
articulating  by  a  prominent  rounded  head  with  the  spbenotic 
and  pterotic.  It  is  united  in  front  with  the  meta-pterygoid 
and  symplectic,  and  sends  off  behind  a  strong  process  which 
articulates  with  the  opercular.  The  symplectic  is  a  long 
somewhat  triangular  bone  drawn  out  in  front  into  a  process 
which  fits  into  a  groove  on  the  inner  surface  of  the  quadrate. 
The  distal  portion  of  the  hyoid  arch  is  strongly  developed  and 
consists  of  first  the  inter-hyal  (fig.  12,  11),  a  short  bony  rod, 
which  articulates  dorsally  with  a  patch  of  cartilage  intervening 
between  the  posterior  part  of  the  hyomandibular  and  the  sym- 
plectic. Below  it  is  united  with  the  apex  of  the  triangular 
epi-hyal,  a  bone  suturally  connected  with  the  large  cerato- 
hyal  (fig.  12,  13)  which  unites  distally  with  two  small  hypo- 
hyals.  To  the  cerato-hyal  are  attached  a  series  of  seven 
strong  curved  cylindrical  rods,  the  branchiostegal  rays.  The 
first  of  these  is  the  smallest  and  they  increase  in  size  up  to  the 
last.  The  four  dorsal  ones  are  attached  to  the  outer  surface 
of  the  cerato-hyal,  the  three  ventral  ones  to  its  inner  surface. 


THE  SKELETON  OF  CODFISH.  BRANCHIAL  ARCHES.  101 

Interposed  between  the  hypo-hyals  of  the  two  sides  is  an 
unpaired  somewhat  triangular  plate,  the  uro-hyal  or  basi- 
branchiosteyal  (fig.  12,  15). 

THE    BRANCHIAL    ARCHES. 

The  branchial  arches  are  five  in  number  and  consist  of 
the  following  parts  on  each  side.  The  dorsal  end  is  formed  of 
the  supra-pharyngeal  bone,  a  large  irregular  bone  covered 
ventrally  with  teeth  of  a  fair  size,  and  representing  the  fused 
pharyngo-branchials  of  the  four  anterior  arches.  Its  external 
surface  is  continuous  with  four  small  epi-branchials  which 
pass  horizontally  backwards  and  outwards.  Their  distal  ends 
meet  four  long  cerato-branchials  which  are  directed  for- 
wards and  inwards  and  form  the  principal  part  of  the  arches. 

Each  of  the  first  three  cerato-branchials  articulates  ven- 
trally with  a  hypo-branchial,  and  the  hypo-branchials  of 
the  two  sides  are  united  in  the  middle  line  by  an  unpaired 
basi-branchial.  The  third  hypo-branchial  is  much  flattened. 
The  fourth  cerato-branchial  is  united  by  cartilage  with  the 
posterior  surface  of  the  third  hypo-branchial,  which  it  meets 
near  the  middle  line. 

The  fifth  arch  consists  only  of  the  cerato-branchial,  a  wide 
structure  covered  with  teeth  and  generally  called  the  inferior 
pharyngeal  bone. 

The  skeleton  of  the  operculum  consists  of  the  same  four 
bones  as  in  the  Salmon,  namely  the  opercular,  the  infra- 
opercular,  the  pre-opercular  and  the  sub-opercular.  Of  these 
the  anterior  bone,  the  pre-opercular,  is  the  largest,  while  the 
infra-opercular  is  the  smallest.  The  opercular  has  a  facet  for 
articulation  with  the  hyomandibular. 

2.     THE  APPENDICULAR  SKELETON. 

THE  PECTORAL  GIRDLE. 

This  is  of  a  highly  specialised  type.  Membrane  bones  are 
greatly  developed,  and  the  cartilage  bones,  the  scapula  and 
coracoid,  are  much  reduced  in  size  and  importance. 


102 


THE  VERTEBRATE  SKELETON. 


The    largest   bone  in  the    shoulder  girdle  is  the  clavicle 
(tig.  13,  3),  which  is  irregularly  crescent  shaped,  thick  in  front 


FIG.  13.     THE  EIGHT  HALF  or  THE  PECTORAL  GIRDLE  AND  RIGHT 
PECTORAL  FIN  OF  A  COD  (Gadus  morrhua)  x  \  (Brit.  Mus.). 

post-temporal.  5.  scapula, 

supra-clavicle.  6.  post-clavicle, 

clavicle.  7.  bracbial  ossicles, 

coracoid.  8.  dermal  fin-rays. 


and  tapering  off  behind.  To  the  outer  side  of  its  upper  part 
is  attached  a  thick  cylindrical  bone,  the  supra-clavicle,  which 
passes  upwards  and  is  connected  with  a  strong  V  shaped 
bone,  the  post-temporal.  The  apex  of  the  V  meets  the  supra- 
clavicle,  the  inner  limb  articulates  with  the  epi-otic  process, 
the  outer  with  the  parotic  process.  Projecting  downwards  from 
the  upper  part  of  the  clavicle  is  a  long  bony  rod,  flattened 


THE   SKELETON    OF   THE   CODB'ISH.      THE    FINS.        103 

proximally  and   cylindrical  and  pointed  distally,  this  is  the 
post-clavicle  (fig.  13,  6). 

The  scapula  (fig.  13,  5)  is  a  small  irregular  plate  of  bone 
attached  to  the  inner  side  of  the  middle  of  the  clavicle.  The 
coracoid1  is  a  larger  plate  of  similar  character,  irregularly 
triangular  in  shape,  attached  to  the  inner  side  of  the  clavicle 
immediately  below  the  scapula.  The  scapula  and  coracoid 
bear  the  pectoral  fin. 

THE  PECTORAL  FINS. 

Each  of  these  consists  of  four  small  irregular  bones,  the 
brachial  ossicles  (fig.  13,  7),  bearing  a  series  of  about  nineteen 
dermal  Jin-rays.  The  brachial  ossicles  represent  the  reduced 
and  modified  radialia  and  basalia  of  cartilaginous  fish  such  as 
the  dogfish.  The  fin-rays  (fig.  13,  8)  which  form  the  whole 
external  portion  of  the  fin  are  long  slender  rods  having 
essentially  the  same  character  as  those  of  the  unpaired  fins. 

THE  PELVIC  GIRDLE. 

The  pelvic  girdle  in  the  Cod  as  in  other  Teleosteans  is 
entirely  absent,  its  place  being  taken  by  the  enlarged  basi- 
pterygia  of  the  fins. 

THE  PELVIC  FINS. 

These  have  a  very  anomalous  position  in  the  Cod,  being 
attached  to  the  throat  in  front  of  the  pectoral  girdle.  Each 
consists  of  a  basal  portion,  the  basi-pterygium,  and  of  a 
number  of  dermal  rays.  The  basi-pterygium  consists  of  an 
expanded  ventral  portion  which  meets  its  fellow  below  in  the 
middle  line,  and  to  which  the  rays  are  attached,  and  of  an  in- 
wardly-directed dorsal  portion  which  also  meets  its  fellow  and 
is  imbedded  in  the  flesh.  The  rays  are  six  in  number  and 
are  long  slender  structures  similar  to  those  of  the  other  fins. 

1  According  to  G.  Swirski,  Sckultergurtel  des  Hechtes,  Dorpat,  1880, 
the  true  coracoid  is  aborted,  and  the  so-called  coracoid  of  Teleosteans  is 
really  the  precoracoid. 


CHAPTER   VIII. 

GENERAL   ACCOUNT   OF    THE    SKELETON   IN 
FISHES1. 

EXOSKELETON. 

The  most  primitive  type  of  exoskeleton  is  that  found  in 
Elasmobranchs  and  formed  of  placoid  scales;  these  are  tooth- 
like  structures  consisting  of  dentine  and  bone  capped  with 
enamel,  and  have  been  already  described  (p.  4).  In  most 
Elasmobranchs  they  are  small  and  their  distribution  is  fairly 
uniform,  but  in  the  Thornback  skate,  Raia  clavata,  they  have 
the  form  of  larger,  more  scattered  spines.  In  adult  Holo- 
cephali  and  in  Polyodon  and  Torpedo  there  is  no  exoskeleton, 
in  young  Holocephali,  however,  there  are  a  few  small  dorsal 
ossifications. 

The  plates  or  scales  of  many  Ganoids  may  have  been 
formed  by  the  gradual  fusion  of  elements  similar  to  these 
placoid  scales,  and  often  bear  a  number  of  little  tooth-like 
processes.  In  Lepidosteus,  Polypterus,  and  .many  extinct 
species,  these  ganoid  scales,  which  are  rhomboidal  in  form 
and  united  to  one  another  by  a  peg  and  socket  articulation, 
enclose  the  body  in  a  complete  armour.  In  Trissolepis  part  of 
the  tail  is  covered  by  rhomboidal  scales,  while  rounded  scales 
cover  the  trunk  and  remainder  of  the  tail.  Acipenser  and 
Scaphirhynchus  have  large  dermal  bony  plates  which  are  not 
rhomboidal  in  shape  and  do  not  cover  the  whole  body.  In 

1  The  following  general  works  on  fishes  may  be  referred  to :  Bashford 
Dean,  Fishes,  Living  and  Fossil,  New  York,  1895.  A.  Giinther,  An 
Introduction  to  the  Study  of  Fishes,  Edinburgh,  1880.  A.  A.  W.  Hubrecht 
and  M.  Sagemehl,  Fische  in  Bronn's  Classen  und  Ordnungen  des  Thier- 
reichs,  Band  vi.  Leipzig,  1876. 


THE  SKELETON  IN  FISHES.      SCALES  AND  FIN-RAYS.     105 

Acipenser  a  single  row  extends  along  the  middle  of  the  back 
and  two  along  each  side. 

The  majority  of  Teleosteans  have  thin  flattened  scales 
which  differ  from  those  of  Ganoids  in  being  entirely  meso- 
dermal  in  origin,  containing  no  enamel.  There  are  two  prin- 
cipal types  of  Teleostean  scales,  the  cycloid  and  ctenoid.  A 
cycloid  scale  is  a  flat  thin  scale  with  concentric  markings 
and  an  entire  posterior  margin.  A  ctenoid  scale  differs  in 
having  its  posterior  margin  pectinate.  The  Dipnoi  have  over- 
lapping cycloid  scales.  The  rounded  scales  of  Amia  and  of  many 
fossil  ganoids  such  as  Holoptychius  are  shaped  like  cycloid 
scales,  but  differ  from  them  in  being  more  or  less  coated  with 
enamel.  In  Eels  and  some  other  Teleosteans  the  scales  are 
completely  degenerate  and  have  almost  disappeared.  Some 
Teleosteans,  like  Diodon  hystrix,  have  scales  with  triradiate 
roots  from  which  arise  long  sharp  spines  directed  backwards. 
These  scales,  which  resemble  teeth,  contain  no  enamel ;  they 
become  erect  when  the  fish  inflates  its  body  into  a  globular 
form.  Many  Siluroids  have  dermal  armour  in  the  form  of 
large  bony  plates  which  are  confined  to  the  anterior  part 
of  the  body.  In  Ostracion  the  whole  body  is  covered  by 
hexagonal  plates,  closely  united  together. 

The  fin-rays  are  structures  of  dermal  origin  which  entirely 
or  partially  support  the  unpaired  fins,  and  assist  the  bony 
or  cartilaginous  endoskeleton  in  the  support  of  the  paired  fins. 

In  Elasmobranchs,  Dipnoi,  and  Chondrosteous  ganoids  the 
skeletons  of  the  fins  are,  as  a  rule,  about  half  of  exoskeletal, 
half  of  endoskeletal  origin,  the  proximal  and  inner  portion 
being  cartilaginous  and  endoskeletal,  the  distal  and  outer  portion 
being  exoskeletal,  and  consisting  of  horny  or  of  more  or  less 
calcified  fin-rays.  In  bony  Ganoids  and  Teleosteans  the  endo- 
skeletal parts  are  greatly  reduced  and  the  fins  come  to  consist 
mainly  of  the  fin-rays,  which  are  ossified  and  frequently  become 
flattened  at  their  distal  ends. 

The  fin-rays  of  the  ventral  part  of  the  caudal  fin  are  carried 


106  THE  VERTEBRATE  SKELETON. 

by  the  haemal  arches ;  those  of  the  dorsal  and  anal  fins  and 
of  the  dorsal  part  of  the  caudal  fin  generally  by  interspinous 
bones,  which  in  adult  Teleosteaiis  alternate  with  the  neural 
and  haemal  spines.  In  Dipnoi  these  interspinous  bones  arti- 
culate with  the  neural  and  haemal  spines.  In  many  Siluroids 
the  anterior  rays  of  the  dorsal  and  pectoral  fins  are  developed 
into  large  spines  which  often  articulate  with  the  endoskeleton,  or 
are  sometimes  fused  with  the  dermal  armour  plates.  Similar 
spines  may  occur  in  Ganoids  in  front  of  both  the  dorsal  and 
anal  fins.  Polypterus  has  a  small  spine  or  fulcrum  in  front  of 
each  segment  of  the  dorsal  fin.  Such  spines  are  often  found 
fossilised,  and  are  known  as  iclithyodorulites. 

Similar  spines  are  found  in  many  Elasmobranchs,  but  they 
are  simply  inserted  in  the  fiesh,  not  articulated  to  the  endo- 
skeleton. They  also  differ  from  the  spines  of  Teleosteans 
and  Ganoids  in  the  fact  that  they  are  covered  with  enamel, 
and  often  have  their  edges  serrated  like  teeth.  In  the  extinct 
Acanthodii  they  generally  occur  in  front  of  all  the  fins,  paired 
and  unpaired. 

In  Trygon,  the  Sting-ray,  the  tail  bears  a  serrated  spine 
which  is  used  for  purposes  of  offence  and  defence.  Many 
ichthyodorulites  may  have  been  spines  of  this  nature  fixed  to 
the  tail,  rather  than  spines  situated  in  front  of  the  fins.  The 
spines,  which  are  always  found  in  front  of  the  dorsal  fin  in 
Holocephali,  agree  with  those  of  Elasmobranchs  in  containing 
enamel,  and  with  those  of  Teleosteans  in  being  articulated  to 
the  endoskeleton. 

TEETH. 

The  teeth  of  fish1  are  subject  to  a  very  large  amount  of 
variation,  perhaps  to  more  variation  than  are  those  of  any 
other  class  of  animals.  Sometimes,  as  in  adult  Sturgeons, 
they  are  entirely  absent,  sometimes  they  are  found  on  all  the 

i  See  W.  G.  Eidewood,  Nat.  Sci.  vol.  vin.  1896,  p.  380.  Full  references 
are  there  given  to  the  literature  of  the  subject. 


THE    SKELETON    IN    FISHES.      THE   TEETH. 


107 


bones  of  the  mouth,  and  also  on  the  hyoid  and  branchial 
arches.  The  teeth  are  all  originally  developed  in  the  mucous 
membrane  of  the  mouth,  but  they  afterwards  generally  become 


5-' 


FIG.  14.    DIAGRAM  OF  A  SECTION  THROUGH  THE  JAW  OF  A  SHARK  (Odontaspis 


americanus)    showing    the 
specimen  and  diagram). 

1.  teeth  in  use. 

2.  teeth  in  reserve. 

3.  skin. 

4.  cartilage  of  the  jaw. 

5.  encrusting     calcification 


succession    of    teeth   (Brit.    Mus.    from 

cartilage. 

6.  connective  tissue. 

7.  mucous    membrane    of    the 

mouth, 
of 


attached  to  firmer  structures,  especially  to  the  jaws.  In 
Elasmobranchs,  however,  they  are  generally  simply  imbedded 
in  the  tough  fibrous  integument  of  the  mouth.  Their  attach- 
ment to  the  jaws  may  take  place  in  three  different  ways. 

(1)  By  an  elastic  hinge-joint,  as  in  the  Angler  (Lophius), 
and  the  Pike  (Esox  lucius).     In  the  Angler  the  tooth  is  held 
by  a  fibrous  band  attaching  its  posterior  end  to  the  subjacent 
bone,  in  the  Pike  by  uncalcified  elastic  rods  in  the  pulp  cavity. 

(2)  By  ankylosis,  i.e.  by  the  complete  union  of   the  cal- 
cined tooth  substance  with  the  subjacent  bone.     This  is  the 
commonest  method  among  fish. 


108 


THE  VERTEBRATE  SKELETON. 


(3)  By  implantation  in  sockets.  This  method  is  not  very 
common  among  fish.  The  teeth  are  sometimes,  as  in  -Lepi- 
dosteus,  ankylosed  to  the  base  of  the  socket.  In  this  genus 
there  is  along  each  ramus  of  the  mandible  a  median  row  of 
large  teeth  placed  in  perfect  sockets,  and  two  irregular  lateral 
rows  of  small  teeth  ankylosed  to  the  jaw. 

Dentine,  enamel  and  cement  are  all  represented  in  the  teeth 
of  fishes,  but  the  enamel  is  generally  very  thin,  and  cement  is 
but  rarely  developed.  Dentine  forms  the  main  bulk  of  the 
teeth;  it  is  sometimes  of  the  normal  type,  but  generally  differs 
from  that  in  higher  vertebrates  in  being  vascular,  and  is 
known  as  vasodentine.  A  third  type  occurs,  known  as  osteo- 
dentine ;  it  is  traversed  by  canals  occupied  by  marrow,  and  is 
closely  allied  to  bone. 


FIG.  15.    PAKT  OF  THE  LOWEB  JAW  OF  A  SHABK  (Galeus) 
(from  OWEN  after  ANDREA. 


1.  teeth  in  use. 

2.  reserve  teeth  folded  back. 

3.  part  of  the  caudal  spine  of 


a  Sting-ray  (Trygon)  which  has 
pierced  the  jaw  and  affected  the 
growth  of  the  teeth. 


The  teeth  are  generally  continually  renewed  throughout  life, 
but  sometimes  one  set  persists. 

The   teeth    of    Selachii  are  fundamentally  identical  with 


THE   SKELETON    IN   FISHES.      THE   TEETH.  109 

placoid  scales.  They  are  developed  from  a  layer  of  dental  germs 
which  occurs  all  over  the  surface  of  the  skin,  except  in  the 
region  of  the  lips.  At  this  point  the  layer  of  tooth-producing 
germs  extends  back  into  the  mouth,  being  projected  by  a  fold 
of  the  mucous  membrane  (fig.  14,  7).  Here  new  teeth  are 
successively  formed,  and  as  they  grow  each  is  gradually 
brought  into  a  position  to  take  the  place  of  its  predecessor 
by  the  shifting  outwards  of  the  gum  over  the  jaw.  Owing  to 
this  arrangement  sharks  have  practically  an  unlimited  supply 
of  teeth  (figs.  14  and  15). 

Two  principal  types  of  teeth  are  found  in  ELASMOBRANCHS. 
In  Sharks  and  Dogfish,  on  the  one  hand,  the  teeth  are  very 
numerous,  simple,  and  sharp-pointed,  and  are  with  or  without 
serrations  and  lateral  cusps.  Many  Rays  and  fossil  Elasmo- 
branchs,  on  the  other  hand,  have  broad  flattened  teeth  adapted 
for  crushing  shells.  Intermediate  conditions  occur  between 
these  two  extremes.  Thus  in  Cestracion  and  many  extinct 
sharks,  such  as  Acrodus,  while  the  median  teeth  are  sharp, 
the  lateral  teeth  are  more  or  less  flattened  and  adapted  for 
crushing.  In  various  species  belonging  to  the  genus  Raia  the 
teeth  of  the  male  are  sharp,  while  those  of  the  female  are  blunt. 
A  very  specialised  dentition  is  met  with  in  the  Eagle-rays 
(Myliobatidae),  in  which  the  jaws  are  armed  with  flattened 
angular  tooth-plates,  arranged  in  seven  rows,  forming  a  com- 
pact pavement ;  the  plates  of  the  middle  row  are  very  wide 
and  rectangular,  those  of  the  other  rows  are  much  smaller  and 
hexagonal.  Lastly,  in  Cochliodus  the  individual  crushing 
teeth  are  fused,  forming  two  pairs  of  spirally-coiled  dental 
plates  on  each  side  of  each  jaw.  Pristis,  the  Saw-fish,  has  a 
long  flat  cartilaginous  snout,  bearing  a  double  row  of  persist- 
ently-growing teeth  planted  in  sockets  along  its  sides.  Each 
tooth  consists  of  a  number  of  parallel  dentinal  columns,  united 
at  the  base,  but  elsewhere  distinct. 

In  the  HOLOCEPHALI — Ckimaera,  Hariotta  and  Callorhyn- 
chus — only  three  pairs  of  teeth  or  dental  plates  occur,  two 


110          THE  VERTEBRATE  SKELETON. 

pairs  in  the  upper  jaw,  one  in  the  lower.  These  structures 
persist  throughout  life  and  grow  continuously.  The  upper 
tooth  structures  are  attached  respectively  to  the  ethmoid  or 
vomerine  region  of  the  skull,  and  to  the  palato-pterygoids.  The 
vomerine  teeth  are  small,  while  those  attached  to  the  mandible 
and  the  palato-pterygoid  region  are  large  and  bear  several 
roughened  ridges  adapted  for  grinding  food.  The  teeth  of 
the  two  opposite  sides  of  the  jaw  meet  in  a  median  symphysis. 
The  teeth  of  Chimaera  are  more  adapted  for  cutting,  those  of 
Callorhynchus  for  crushing.  Many  extinct  forms  are  known, 
some  of  whose  teeth  are  intermediate  in  structure  between 
those  of  Chimaera  and  Callorhynchus. 

The  teeth  of  GANOIDS  are  also  extremely  variable.  Among 
living  forms,  the  Holostei  are  more  richly  provided  with  teeth 
than  are  any  other  fishes,  as  they  may  occur  on  the  pre- 
maxillae,  maxillae,  palatines,  pterygoids,  parasphenoid,  voiners, 
dentaries,  and  splenials.  Among  the  Chondrostei,  on  the  other 
hand,  the  adult  Acipenseridae  are  toothless ;  small  teeth  how- 
ever occur  in  the  larval  sturgeon,  and  in  Polyodon  many 
small  teeth  are  found  attached  merely  to  the  mucous  membrane 
of  the  jaws.  Many  fossil  Ganoids  have  numerous  flattened  or 
knob-like  teeth,  borne  on  the  maxillae,  palatines,  vomers  and 
dentaries.  Others  have  a  distinctly  heterodont  dentition. 
Thus  in  Lepidotus  the  prernaxillae  bear  chisel-like  teeth,  while 
knob-like  teeth  occur  on  the  maxillae,  palatines  and  vomers. 
In  Rhizodus  all  the  teeth  are  pointed,  but  while  the  majority 
are  small  a  few  very  large  ones  are  interspersed. 

In  TELEOSTEANS,  too,  the  teeth  are  eminently  variable  both 
in  form  and  mode  of  arrangement.  They  may  be  simple  and 
isolated,  or  compound,  and  may  be  borne  on  almost  any  of  the 
bones  bounding  the  mouth  cavity,  and  also  as  in  the  Pike,  on 
the  hyoid  and  branchial  arches.  The  splenial  however  never 
bears  teeth  and  the  pterygoid  and  parasphenoid  only  rarely, 
thus  differing  from  the  arrangement  in  the  Holostei. 

The  isolated  teeth  are  generally  conical  in  form  and  are 


THE    SKELETON    IN   FISHES.      THE    TEETH.  Ill 

ankylosed  to  the  bone  that  bears  them.  Such  teeth  are, 
with  a  few  exceptions  such  as  Balistes,  not  imbedded  in 
sockets  nor  replaced  vertically. 

In  some  fish  beak-like  structures  occur,  formed  partly  of 
teeth,  partly  of  the  underlying  jaw  bones.  These  beaks  are  of 
two  kinds  :  (1)  In  Scarus,  the  parrot  fish,  the  premaxillae  and 
dentaries  bear  numerous  small,  separately  developed  teeth, 
which  are  closely  packed  together  and  attached  by  their 
proximal  ends  to  the  bone,  while  their  distal  ends  form  a 
mosaic.  Not  only  the  teeth  but  the  jaws  which  bear  them 
are  gradually  worn  away  at  the  margins,  while  both  grow 
continuously  along  their  attached  edge.  (2)  In  Gymnodonts, 
e.g.  Diodon,  the  beaks  are  formed  by  the  coalescence  of  broad 
calcified  horizontal  plates,  which  when  young  are  free  and 
separated  from  one  another  by  a  considerable  interval. 

In  some  Teleosteans  the  differentiation  of  the  teeth  into 
biting  teeth  and  crushing  teeth  is  as  complete  as  in  Lepi- 
dosteus.  Thus  in  the  Wrasse  (Labrus),  the  jaws  bear  conical 
slightly  recurved  teeth  arranged  in  one  or  two  rows,  with  some 
of  the  anterior  ones  much  larger  than  the  rest.  The  bones  of 
the  palate  are  toothless,  while  both  upper  and  lower  pharyngeal 
bones  are  paved  with  knob-like  crushing  teeth ;  such  pharyn- 
geal teeth  occur  also  in  the  Carp  but  are  attached  only  to  the 
lower  pharyngeal  bone,  the  jaw  bones  proper  being  toothless. 

In  DIPNOI  the  arrangement  of  the  teeth  is  very  similar  to 
that  in  Holocephali.  The  mandible  bears  a  single  pair  of 
grinding  teeth  attached  to  the  splenials,  and  a  corresponding 
pair  occur  on  the  palato-pterygoids.  In  front  of  these  there 
are  a  pair  of  small  conical  vornerine  teeth  loosely  attached  to  the 
ethmoid  cartilage.  The  palato-pterygoid  teeth  of  Ceratodus 
are  roughly  semicircular  in  shape  with  a  smooth  convex  inner 
border,  and  an  outer  border  bearing  a  number  of  strongly 
marked  ridges.  The  teeth  of  the  extinct  Dipteridae  resemble 
those  of  Ceratodus  but  are  more  complicated. 


112  THE  VERTEBRATE  SKELETON. 

ENDOSKELETON. 

SPINAL  COLUMN  l. 

The  spinal  column  of  fishes  is  divisible  into  only  two 
regions,  a  caudal  region  in  which  the  haemal  arches  or  ribs 
meet  one  another  ventrally,  and  a  precaudal  region  in  which 
they  do  not  meet. 

The  various  modifications  of  the  spinal  column  in  fishes 
«an  be  best  understood  by  comparing  them  with  the  arrange- 
ment in  the  simplest  type  known,  namely  Amphioxus.  In 
Amphioxus  the  notochord  is  immediately  surrounded  by  a 
structureless  cuticular  layer,  the  chordal  sheath.  Outside  this 
is  the  skeletogenous  layer,  which  in  addition  to  surrounding 
the  notochord  and  chordal  sheath  embraces  the  nerve  cord 
dorsally,  and  laterally  sends  out  septa  forming  the  myomeres. 

The  CARTILAGINOUS  GANOIDS 2  Acipenser,  Polyodon  and 
Scaphirhynchus  are  the  simplest  fishes  as  regards  their  spinal 
column.  The  notochord  remains  permanently  unconstricted 
and  is  enclosed  in  a  chordal  sheath,  external  to  which  is  the 
skeletogenous  layer.  In  this  layer  the  development  of  carti- 
laginous elements  has  taken  place.  In  connection  with  each 
neuromere,  or  segment  as  determined  by  the  points  of  exit  of 
the  spinal  nerves,  there  are  developed  two  pairs  of  ventral 
cartilages,  the  ventral  arches  (basiventralia)  and  intercalary 
pieces  (interventralia) ;  and  at  least  two  pairs  of  dorsal  pieces, 
the  neural  arches  (basidorsalia)  and  intercalary  pieces  (inter- 
dorsalia).  The  lateral  parts  of  the.  skeletogenous  layer  do  not 
become  converted  into  cartilage,  so  there  are  no  traces  of 
vertebral  centra.  The  ventral  or  haemal  arches  meet  one 
another  ventrally  and  send  out  processes  to  protect  the  ven- 
tral vessels.  The  neural  arches  do  not  meet,  but  are  united 
by  a  longitudinal  elastic  band. 

In  Cartilaginous  ganoids  the  only  indications  of  metameric 

1  See  H.  Gadow  and  E.  C.  Abbott,  Phil.  Trans,  vol.  186  (1895)  B. 
pp.  163—221. 

2  C.  Hasse,  Zeitschr.  wiss.  Zool.  LVII.  1893,  p.  76. 


THE    SKELETON    IN    FISHES.      VERTEBRAL   COLUMN.     113 

segmentation  are  found  in  the  neural  and  haemal  arches.  The 
case  is  somewhat  similar  with  the  Holocephali  and  Dipnoi. 

In  the  HOLOCEPHALI  the  nqtochord  grows  persistently 
throughout  life,  and  is  of  uniform  diameter  throughout  the 
whole  body  except  in  the  cervical  region  and  in  the  gradually 
tapering  tail.  The  chordal  sheath  is  very  thick  and  includes  a 
well-marked  zone  of  calcification  which  separates  an  outer  zone  of 
hyaline  cartilage  from  an  inner  zone.  There  are  also  a  number 
of  cartilaginous  pieces  derived  from  the  skeletogenous  layer 
which  are  arranged  in  two  series,  a  dorsal  series  forming  the 
neural  arches  and  a  ventral  series  forming  the  haemal  arches. 
These  do  not,  except  in  the  cervical  region,  meet  one  another 
laterally  round  the  notochord  and  form  centra.  To  each 
neuromere  there  occur  a  pair  of  basidorsals,  a  pair  of  inter- 
dorsals,  and  one  or  two  supradorsals.  In  the  tail  the  arrange- 
ment is  irregular. 

In  the  DIPNOI  as  in  the  Holocephali  the  notochord  grows 
persistently  and  uniformly,  and  the  chordal  sheath  is  thick 
and  cartilaginous  though  there  are  no  metamerically  arranged 
centra.  The  neural  and  haemal  arches  and  spines  are  cartila- 
ginous and  interbasalia  (intercalary  pieces)  are  present.  The 
basidorsalia  and  basiventralia  do  not  in  Ceratodus  meet 
round' the  notochord  and  enclose  it  except  in  the  anterior  part 
of  the  cervical  and  posterior  part  of  the  caudal  region. 

In  ELASMOBRANCHII  the  chordal  sheath  is  weak  and  the 
skeletogenous  layer  strong.  Biconcave  cartilaginous  vertebrae 
are  developed,  and  as  is  the  case  in  most  fishes,  constrict  the 
notochord  vertebrally. 

Two  distinct  types  of  vertebral  column  can  be  distinguished 
in  Elasmobranchs ! : 

1.     In  many  extinct  forms  and  in  the  living  Notidanidae, 

1  C.  Hasse,  Das  naturliche  System  der  Elasmobranchier  auf  Grundlage 
des  Baues  und  der  Entwickelung  ihrer  Wirbelsdule,  Jena,  1879  and  1885, 
and  "Die  fossilen  Wirbel,  Morph.  Studieu  i. — iv.," Morphol.  Jahrb.  Bd.  n. 
in.  and  iv.  1876 — 78. 

R.  8 


114          THE  VERTEBRATE  SKELETON. 

Cestracion,  and  Squatina,  the  dorsal  and  ventral  arches  do  not 
meet  one  another  laterally  round  the  centrum,  and  conse- 
quently readily  come  away  from  it. 

2.  In  most  living  Elasmobranchs  the  arches  meet  laterally 
round  the  centrum. 

The  vertebrae  are  never  ossified  but  endochondral  calcifica- 
tion nearly  always  takes  place,  though  it  very  rarely  reaches 
the  outer  surface  of  the  vertebrae.  Elasmobranchs  are  some- 
times subdivided  into  three  groups  according  to  the  method 
in  which  this  calcification  takes  place  : 

1.  Cyclospondyli   (Scymniis,  Acanthias),  in  which  the 
calcified  matter  is  deposited  as  one  ring  in  each  vertebra. 

2.  Tectospondyli   (Squatina,  Raia,   Trygon),  in  which 
there  are  several  concentric  rings  of  calcification. 

3.  Asterospondyli  (Notidanidae,  Scyllium,  Cestracion), 
in  which  the  calcified  material  instead  of  forming  one  simple 
ring,  extends  out  in  a  more  or  less  star-shaped  manner. 

In  Heptanchus  the  length  of  the  vertebral  centra  in  the 
middle  of  the  trunk  is  double  that  in  the  anterior  and  posterior 
portions,  and  as  the  length  of  the  arches  does  not  vary,  the 
long  centra  carry  more  of  them  than  do  the  short  centra. 

In  many  Rays  the  skull  articulates  with  the  vertebral 
column  by  distinct  occipital  condyles. 

In  BONY  GANOIDS  the  skeletogenous  layer  becomes  calcified 
ectochondrally  in  such  a  way  that  the  notochord  is  pinched  in 
at  intervals,  and  distinct  vertebrae  are  produced.  Ossification 
of  the  calcified  cartilage  rapidly  follows.  In  Amia  the  verte- 
brae are  biconcave,  in  Lepidosteus  they  are  opisthocoelous,  cup 
and  ball  joints  being  developed  between  the  vertebrae  in  a 
manner  unique  among  fishes.  The  notochord  entirely  disap- 
pears in  the  adult  Lepidosteus,  but  at  one  stage  in  larval  life 
it  is  expanded  vertebrally  and  constricted  intervertebrally  in 
the  manner  usual  in  the  higher  vertebrata,  but  unknown 
elsewhere  among  fishes. 


THE   SKELETON   IN    FISHES.      THE    FINS.  115 

The  tail  of  Amia  is  remarkable  from  the  fact  that  as  a 
rule  to  each  neuromere,  as  determined  by  the  exit  of  the 
spinal  nerves,  there  are  two  centra,  a  posterior  one  which 
bears  nothing,  and  an  anterior  one  which  bears  the  neural  and 
haemal  arches,  these  being  throughout  the  vertebral  column 
connected  with  the  centra  by  cartilaginous  discs. 

In  most  TELEOSTEANS  but  not  in  the  Plectognathi  the  neural 
arches  are  continuous  with  the  centra,  which  are  nearly  always 
deeply  biconcave. 

In  some  cases  many  of  the  anterior  vertebrae  are  anky- 
losed  together  and  to  the  skull.  The  vertebrae  often  articu- 
late with  one  another  by  means  of  obliquely  placed  flattened 
surfaces,  the  zygapophyses.  The  centrum  in  early  stages  of 
development  is  partially  cartilaginous,  but  the  neural  arches 
and  spines  in  the  trunk  at  any  rate,  pass  directly  from  the 
membranous  to  the  osseous  condition. 

FINS. 

The  most  primitive  fins  are  undoubtedly  the  unpaired  ones, 
which  probably  originally  arose  as  ridges  or  folds  of  skin 
along  the  mid-dorsal  line  of  the  body,  and  passed  thence 
round  the  posterior  end  on  to  the  ventral  surface,  partially 
corresponding  in  position  and  function  to  the  keel  of  a  ship. 

In  long  'fish'  which  pass  through  the  water  with  an 
undulating  motion  such  simple  continuous  fins  may  be  the 
only  ones  found,  as  in  Myxine.  To  support  these  median  fins 
skeletal  structures  came  to  be  developed ;  these  show  two 
very  distinct  forms,  viz.  cartilaginous  endoskeletal  pieces,  the 
radialia,  and  horny  exoskeletal  fibres,  the  Jin-rays.  Me- 
chanical reasons  caused  the  fin  to  become  concentrated  at 
certain  points  and  reduced  at  intervening  regions.  Thus  a 
terminal  caudal  fin  arose  and  became  the  chief  organ  of 
propulsion,  and  the  dorsal  and  ventral  fins  became  specialised 
to  act  as  balancing  organs. 

In  some  of  the  earlier  Elasmobranchs,  the  Pleuracanthidae, 

8—2 


116  THE  VERTEBRATE  SKELETON. 

the  endoskeletal  cartilaginous  radialia  are  directly  con- 
tinuous with  outgrowths  from  the  dorsal  and  ventral  arches 
of  the  vertebrae,  and  form  the  main  part  of  the  fin.  In 
later  types  of  Elasmobranchs  the  horny  exoskeletal  fin-rays 
have  comparatively  greater  prominence.  In  bony  fish,  as  has 
been  already  stated,  the  horny  fibres  are  replaced  by  bony 
rays  of  dermal  origin,  and  at  the  same  time  complete  reduc- 
tion and  disappearance  of  the  cartilaginous  radialia  takes 
place. 

THE  CAUDAL  FIN. 

The  caudal  region  of  the  spinal  column  in  fishes  is  of 
special  importance.  It  is  distinctly  marked  off  from  the  rest 
of  the  spinal  column  by  the  fact  that  the  ventral  or  haemal 
arches  meet  one  another  and  are  commonly  prolonged  into 
spines,  while  in  the  trunk  region  they  do  not  meet  but  com- 
monly diverge  from  one  another. 

In  some  fish  the  terminal  part  of  the  caudal  region  of  the 
spinal  column  retains  the  same  direction  as  the  rest  of  the 
spinal  column.  The  blade  of  the  caudal  fin  is  then  divided 
into  two  nearly  equal  portions,  and  is  said  to  be  diphycercal. 
This  condition  is  generally  regarded  as  the  most  primitive  one  ; 
it  occurs  in  the  Ichthyotomi,  Holocephali,  all  living  Dipnoi, 
Polypterus  and  some  extinct  Crossopterygii,  and  a  few  Selachii 
and  Teleostei.  It  occurs  also  in  deep-sea  fish  belonging  to 
almost  every  group,  and  under  these  conditions  obviously 
cannot  be  regarded  as  primitive,  but  must  be  looked  on  as 
a  feature  induced  by  the  peculiar  conditions  of  life. 

In  the  great  majority  of  fish  the  terminal  part  of  the 
caudal  region  of  the  spinal  column  is  bent  dorsal  wards,  and 
the  part  of  the  blade  of  the  caudal  fin  which  arises  on  the 
dorsal  surface  is  much  smaller  than  is  that  arising  on  the 
ventral  surface.  Such  a  fin  is  said  to  be  heterocercal. 

Strictly  speaking  all  fish  whose  tails  are  not  diphycercal 
have  heterocercal  tails,  but  the  term  is  commonly  applied 


THE   SKELETON    IN    FISHES.      THE   SKULL.  117 

to  two-bladed  tails  in  which  the  spinal  column  forms  a  definite 
axis  running  through  the  dorsal  blade,  while  the  ventral  blade 
is  enlarged  and  generally  forms  the  functional  part  of  the 
tail.  Such  heterocercal  tails  are  found  in  nearly  all  Elasmo- 
branchii,  together  with  the  living  cartilaginous  Ganoidei, 
and  many  extinct  forms  belonging  to  the  same  order;  Lepi- 
dosteus,  Amia,  and  the  Dipteridae  among  Dipnoi,  have  tails 
which,  though  obviously  heterocercal,  are  not  two-bladed. 

The  vast  majority  of  the  Teleostei  and  some  extinct  Ga- 
noidei have  heterocercal  tails  of  the  modified  type  to  which 
the  term  homocercal  is  applied.  The  hypural  bones  which 
support  the  lower  half  of  the  tail  fin  become  much  enlarged, 
and  frequently  unite  to  form  a  wedge-shaped  bone  which  be- 
comes ankylosed  to  the  last  ossified  vertebral  centrum.  The 
fin-rays  then  become  arranged  in  such  a  way  as  to  produce  a 
secondary  appearance  of  symmetry.  Some  homocercal  fish 
such  as  the  Perch  have  the  end  of  the  notochord  protected 
by  a  calcified  or  completely  ossified  sheath,  the  urostyle,  to 
which  several  neural  and  haemal  arches  may  be  attached,  and 
which  becomes  united  with  the  centrum  of  the  last  vertebra ; 
in  others  such  as  the  Salmon  the  end  of  the  notochord  is  pro- 
tected only  by  laterally  placed  bony  plates. 

THE  SKULL. 

It  is  often  impossible  to  draw  a  hard  and  fast  line  between 
the  cranium  and  the  vertebral  column.  This  is  the  case  for 
instance  in  Acipenser  (fig.  18,  16)  among  Chondrostei,  in  Amia 
among  Holostei,  and  in  Ceratodus  and  Protopterus  among 
Dipnoi.  The  occipital  region  of  the  skull  in  Amia  is  clearly 
formed  of  three  cervical  vertebrae  whose  centra  have  become 
absorbed  into  the  cranium,  while  the  neural  arches  and  spines 
are  still  distinguishable. 

The  simplest  type  of  cranium  is  that  found  in  ELASMO- 
BRANCHS:  it  consists  of  a  simple  cartilaginous  box,  which  is 
generally  immovably  fixed  to  the  vertebral  column,  though 


118 


THE  VERTEBRATE  SKELETON. 


in  some  forms,  like  Scymnus  and  Galeus,  a  joint  is  indicated, 
and  in  others,  such  as  the  Rays,  one  is  fairly  well  developed. 


FIG.   16.     A.    SKULL   OF  Notidanus 


(Brit.   Mus.).      B.    SKULL   OF 


Cestracion  x£  (after  GEGENBAUB).    In  neither  case  are  the  branchial 
arches  shown. 

6.  Meckel's  cartilage. 

7.  teeth. 


1.  rostrum. 

2.  olfactory  capsule. 

3.  ethmo-palatine  process. 

4.  palatine   portion   of  palato- 

pterygo-quadrate  bar. 

5.  quadrate  portion  of  bar. 


8.  labial  cartilage. 

9.  hyomandibular. 
10.     postorbital  process. 

II.     optic  foramen. 


The  cranium  in  Elasmobranchs  is  never  bony,  though  the 
cartilage  is  sometimes  calcined.  It  is  drawn  out  laterally 
into  an  antorbital  process  in  front  of  the  eye,  and  a  post- 


THE   SKELETON    IN    FISHES.      THE   SKULL.  119 

orbital  process  behind  it.  The  nasal  capsules  are  always  carti- 
laginous, and  the  eye,  as  a  general  rule,  has  a  cartilaginous 
sclerotic  investment.  The  cranium  is  often  prolonged  in 
front  into  a  rostrum  which  is  enormously  developed  in  Pristis 
and  some  Rays.  The  cartilaginous  roof  of  the  cranium  is 
rendered  incomplete  by  the  presence  of  a  large  hole,  the  an- 
terior fontanelle. 

Two  pairs  of  labial  cartilages  (fig.  16,  B,  8)  are  often 
present.  They  lie  imbedded  in  the  cheeks  outside  the  anterior 
region  of  the  jaws,  and  are  specially  large  in  Squatina. 

As  regards  the  visceral  arches1  the  simplest  and  most  primi- 
tive condition  of  the  jaws  is  that  of  the  Notidanidae,  in  which 
the  niandibular  and  hyoid  arches  are  entirely  separate.  In 
these  primitive  fishes  the  palato-pterygo-quadrate  bar  articu- 
lates with  the  postorbital  process  (fig.  16,  10),  while  further 
forwards  it  is  united  to  the  cranium  by  the  ethmo-palatine 
ligament.  The  hyoid  arch  is  small  and  is  broadly  overlapped  by 
the  niandibular  arch.  The  term  autostylic  is  used  to  describe 
this  condition  of  the  suspensorium.  From  this  condition  we 
pass  in  the  one  direction  to  that  of  Cestracion  (fig.  16,  B),  in 
which  the  whole  of  the  palato-pterygo-quadrate  bar  has  become 
bound  to  the  cranium,  and  in  the  other  to  that  of  Scyllium. 
In  Scyllium  (fig.  6),  while  the  ethmo-palatine  ligament  is 
retained,  the  postorbital  articulation  of  the  palato-pterygo- 
quadrate  has  been  given  up,  so  that  the  palato-pterygo-quadrate 
comes  to  abut  on  the  hyomandibular  and  is  attached  to  it  by 
ligaments.  The  pre-spiracular  ligament  (fig.  16,  20)  running 
from  the  auditory  capsule  also  assists  in  supporting  the  jaws. 

Lastly  we  come  to  the  purely  hyostylic  condition  met 
with  in  Rays,  in  which  the  niandibular  arch  is  entirely  sup- 
ported by  the  hyomandibular.  In  some  Rays  the  hyoid  is 
attached  to  the  posterior  face  of  the  hyomandibular  near  its 
proximal  end,  and  may  even  come  to  articulate  with  the 
cranium. 

1  See  H.  B.  Pollard,  Anat.  Am.  x.  1894. 


120  THE   VERTEBRATE   SKELETON. 

The  visceral  arches  of  Elasmobranchs  may  be  summa- 
rised as  follows  : — 

1.  The  mandibular  arch,  consisting  of  a  much  reduced 
dorsal  portion,  the  pre-spiracular  ligament,  and  a  greatly  de- 
veloped  ventral   portion   from  which   both  upper   and   lower 
jaws  are  derived.     The  mandible  (Meckel's  cartilage)  is  the 
original  lower  member  of  the  mandibular  arch,  and  from  it 
arises  an   outgrowth  which   forms   the   upper  jaw  or  palato- 
pterygo-quadrate  bar.     In  Scymnus  this  bears  a  few  branchio- 
stegal  rays. 

2.  The  hyoid  arch,  which  consists  of  the  hyomandibular 
and  the  hyoid,  and  bears  branchiostegal  rays  on  its  posterior 
face. 

3.  The  branchial  arches,  generally  five  in  number,  all 
of  which  except  the  last  bear  branchiostegal  rays.     In  the 
Notidanidae    the  Dumber    of   branchial    arches    is    increased 


FIG.  17.     DORSAL  VIEW  OF  THE  BRANCHIAL  ARCHES  OF 

Heptanchus.  (From  GEGENBAUR). 

1.  basi-hyal.  7.     pharyiigo-branchial,  common 

2.  cerato-hyal.  to   the   sixth   and   seventh 

3.  second  hypo -branchial.  arches. 

4.  first  cerato-branchial.  8.     basi-branchial of  second  arch. 

5.  first  epi-branchial.  9.  basi-branchial,  common  to  the 

6.  first  pharyngo-branchial.  sixth  and  seventh  arches. 


THE    SKELETON    IX    FISHES.      THE   SKULL.  121 

beyond  the  normal  series,  thus  in  Hexanchus  there  are  six,  and 
in  Heptanchus  seven.  There  are  six  also  in  Chlamydoselache 
and  Protopterus. 

4.  The  so-called  external  branchial  arches  which  are  carti- 
laginous rods  attached  to  all  the  visceral  arches.  They  are 
especially  large  in  Cestracion. 

The  skull  in  HOLOCEPHALI  is  entirely  cartilaginous.  The 
palato-pterygo-quadrate  bar  is  fixed  to  the  cranium,  and  to 
it  the  mandible  articulates.  There  is  a  well-marked  joint 
between  the  skull  and  the  spinal  column. 

In  living  Cartilaginous  GANOIDS  the  primitive  cartilaginous 
cranium  is  very  massive,  and  is  greatly  prolonged  anteriorly, 
while  posteriorly  it  merges  into  the  spinal  column.  Although  it 
is  mainly  cartilaginous  a  number  of  ossifications  take  place  in 
the  skull,  and  membrane  bones  are  now  found  definitely  de- 
veloped, especially  in  connection  with  the  roof  of  the  cranium. 
In  Acipenser  (fig.  18)  the  ossifications  in  the  cartilage  include 
the  pro-otic,  which  is  pierced  by  the  foramen  for  the  fifth  nerve, 
the  alisphenoid,  orbitosphenoid,  ectethmoid,  palatine,  pterygoid, 
meso-pterygoid,  hyomandibular  (fig.  18,  11),  cerato-hyal,  all  the 
cerato-branchials,  and  the  first  two  epi-branchials.  Most  of 
these  structures  are,  however,  partly  cartilaginous,  though 
they  include  an  ossified  area.  The  membrane  bones  too  of 
Acipenser  are  very  well  developed,  they  include  a  bone  occu- 
pying the  position  of  the  supra-occipital,  and  form  a  complete 
dorsal  cephalic  shield.  Resting  on  the  ventral  surface  are  a 
vomer  and  a  very  large  parasphenoid  (fig.  18,  3).  There  is  a 
bony  operculum  attached  to  the  hyomandibular,  and  membrane 
bones  representing  respectively  the  maxilla  and  dentary  are 
attached  to  the  jaws.  The  suspensorium  is  most  markedly 
hyostylic.  The  palato-pterygo-quadrate  bar  has  a  very  curious 
shape  and  is  quite  separate  from  the  cranium.  It  is  connected 
to  the  hyomandibular  by  a  thick  symplectic  ligament  con- 
taining a  small  bone  homologous  with  the  symplectic  of 
Teleosteans. 


122 


THE  VERTEBRATE  SKELETON. 


Polyodon  differs  much  from  Acipenser,  the  membrane  bones 
not  being  so  well  developed  though  they  cover  the  great  carti- 
laginous snout. 

The  skull  in  Polypterus  (Crossopterygii)  shows  a  great 
advance  towards  the  condition  met  with  in  Teleostei.  The 
cranium  remains  to  a  great  extent  unossified,  and  large  dorsal 
and  ventral  fontanelles  pierce  its  walls.  It  is  covered  by  a 


FIG.  18.  LATERAL  VIEW  OF  THE  SKULL  OF  A  STURGEON  (Acipenser 
sturio).  Nearly  all  the  membrane  bones  have  been  removed  (Brit. 
Mus.). 

palatine. 

hyomandibular. 

pharyngo-branchial. 

epi-branchial. 

cerato-branchial. 

hypo-branchial. 


nasal  cavity. 

orbit. 

parasphenoid. 

vomer. 

pterygoid. 

maxilla.  (The  dotted  line 
running  from  6  passes 
into  the  mouth  cavity.) 

dentary. 

symplectic. 


10. 
11. 
12. 
13. 
14. 
15. 
16. 
17. 
18. 
19. 


coalesced  anterior  vertebrae. 

inter-hyal. 

cerato-hyal. 

rib. 


great  development  of  membrane  bones,  paired  nasals,  frontals, 
parietals,  supra-  and  post-temporals,  and  dermo-supra-occipitals 
among  others  being  present.  The  palato-ptery go- quadrate  bar 
is  fused  to  the  cranium,  and  in  connection  with  it  the  following 
paired  membrane  bones  appear,  palatine,  ecto-,  meso-  and  meta- 
pterygoid,  and  further  forwards  jugal,  vomer,  maxilla  and 
premaxilla.  The  membrane  bones  developed  in  connection 


THE    SKELETON   IN    FISHES.      THE    SKULL.  123 

with  each  ramus  of  the  mandible  are  the  dentary,  angular, 
and  splenial,  in  addition  to  the  cartilage  bone  the  articular. 
Several  large  opercular  bones  occur.  There  are  also  a  pair  of 
large  jugular  or  gular  plates,  and  several  large  opercular  bones. 

In  Bony  Ganoids  both  cartilage  bone  and  membrane 
bone  is  well  developed.  The  pro-otics  and  exoccipitals  are 
well  ossified,  but  the  supra-occipital  and  pterotics  are  not. 
Lateral  ethmoids  are  developed,  and  there  are  ossifications  in 
the  sphenoidal  region  which  vary  in  different  'forms.  The 
place  of  the  cartilaginous  palato-pterygo-quadrate  is  taken  by 
a  series  of  bones,  the  quadrate  behind  and  the  palatine,  ecto-, 
meso-  and  meta-pterygoids  in  front.  In.  Lepidosteus,  however, 
the  palatine  and  pterygoid  are  membrane  bones,  as  they  are 
in  Polypterus  and  the  Frog.  Paired  maxillae,  premaxillae, 
vomers  and  a  parasphenoid  occur  forming  the  upper  jaw  and 
roof  of  the  mouth,  and  a  series  of  membrane  bones  are  found 
investing  the  mandible  and  forming  the  operculum. 

In  Amia1  membrane  bones  are  as  freely  developed  as  they 
are  in  Teleosteans ;  they  include  on  each  side  a  squamosal, 
four  opercular  bones,  a  lachrymal,  a  pre-orbital,  one  or  two 
suborbitals,  two  large  postorbitals  and  a  supratemporal ;  while 
investing  the  mandible,  besides  the  dentary,  splenial,  angular, 
and  supra-angular,  there  is  an  unpaired  jugular.  The  articular 
too  is  double  and  a  mento-meckelian  occurs.  In  Amia  teeth 
are  borne  on  the  premaxillae,  maxillae,  vomers,  palatines  and 
pterygoids. 

Bony  Ganoids  are  the  lowest  animals  in  which  squamosal 
bones  are  found,  and  they  do  not  occur  in  Teleosteans. 

The  suspensoriuin  in  bony  Ganoids,  as  in  the  Chondrostei, 
is  hyostylic,  and  there  are  two  ossifications  in  the  hyoman- 
dibular  cartilage,  viz.  the  hyomandibular,  and  the  symplectic. 

1  T.  W.  Bridge,  "The  Cranial  Osteology  of  Amia  calva,"  J.  Anat. 
Physiol.  norm.  path.  1876,  vol.  xi.  p.  605.  K.  Shufeldt,  "The  Osteology 
of  Amia  calva,"  Ann.  Rep.  of  the  Commissioner  for  Fish  and  Fisheries, 
Washington,  1885. 


124  THE  VERTEBRATE  SKELETON. 

The  skull  of  TELEOSTEI  is  very  similar  to  those  of  Lepidosteus 
and  Amia.  Although  the  bony  skull  is  greatly  developed  and 
very  complicated,  much  of  the  original  cartilaginous  cranium 
often  persists.  Membrane  bones  are  specially  developed  on 
the  roof  of  the  skull  where  they  include  the  parietal,  frontal, 
and  nasal  bones.  The  same  bones  are  developed  in  connection 
with  the  upper  jaw  and  roof  of  the  mouth  as  in  bony  Ganoids, 
but  only  two  membrane  bones  occur  in  the  lower  jaw,  viz.  the 
angular  and'  dentary.  A  number  of  large  ossifications  take 
place  in  the  cartilage  of  the  auditory  capsules.  In  some  forms 
parts  of  the  last  pair  of  branchial  arches  are  broadened  out 
and  form  the  pharyngeal  bones  which  bear  teeth.  The  oper- 
cular  bones  and  those  of  the  upper  and  lower  jaws  are  quite 
comparable  to  those  of  bony  Ganoids. 

A  full  account  of  the  Teleostean  skull  has  been  given  in 
the  case  of  the  Salmon  (pp.  87 — 96)  and  the  Cod  (pp.  96 — 
101). 

In  DIPNOI  the  skull  is  mainly  cartilaginous,  but  both 
cartilage-  and  membrane-bone  occur  also.  Cartilage-bone  is 
found  in  the  ossified  exoccipitals,  while  of  membrane-bones 
Protopterus  has  among  unpaired  bones  a  fronto-parietal,  a 
median  ethmoid,  and  a  parasphenoid,  and  among  paired  bones 
nasals  and  large  supra-orbitals.  The  skull  of  Ceratodus  (fig.  19) 
has  an  almost  complete  roof  of  membrane  bones,  including  some 
whose  homology  is  doubtful.  The  ethmo-vomerine  region  is 
always  cartilaginous,  but  bears  small  teeth.  The  palato- 
pterygo-quadrate  bar  is  ossified  and  firmly  united  to  the 
cranium,  and  the  mandible  articulates  directly  with  it  (auto- 
stylic).  Membrane  bones  are  freely  developed  in  connection 
with  the  mandible,  dentary,  splenial,  and  angular  bones  being 
all  present.  There  are  two  opercular  bones. 

In  the  extinct  Dipteridae  the  cranium  is  very  completely 
covered  with  plates  of  dermal  bone,  and  the  skeleton  in 
general  is  more  ossified  than  is  the  case  in  recent  Dipnoi. 

Six  pairs  of  branchial  arches  occur  in  Protopterus ;  Cera- 


THE   SKELETON    IN    FISHES.      THE    RIBS. 


125 


todus  and   Lepidosiren  have  five,  like  most  other  fish.     The 
branchial  arches  bear  gill  rakers. 


....10 


.-11 


FIG.   19.     DORSAL    (TO   THE   LEFT)  AND  VENTRAL   (TO  THE  RIGHT)  VIEWS 
OP  THE  CRANIUM  OF  Ceratoclus  iiiiolepis  (after  GUNTHER). 


6. 


cartilaginous     part     of  the           7. 

quadrate    with   which  the           8. 

mandible  articulates.  9. 

scleroparietal.  10. 

frontal.  11. 

ethmoid.  12. 

nares.  13. 

orbit.  14. 


pre-opercular  (squamosal). 
second  rib. 
first  rib. 
vomerine  tooth, 
palato-pterygoid  tooth, 
palato-pterygoid. 
parasphenoid. 
interopercular. 


RIBS. 

As  has  been  already  mentioned  (p.  24),  although  ribs 
commonly  appear  to  be  the  cut-off  ends  of  the  transverse  pro- 
cesses, they  are  really  elements  derived  from  the  ventral  or 
haemal  arch. 

In  Elasmobranchii  and  other  cartilaginous  fish  they  have 
the  form  of  small  cartilaginous  structures  imperfectly  separated 


126          THE  VERTEBRATE  SKELETON. 

from  the  diverging  halves  of  the  ventral  arch,  and  are  often 
absent. 

In  Teleostei  and  bony  Ganoids  they  often  have  different  at- 
tachments in  different  parts  of  the  body.  In  the  tail  region  they 
are  not  differentiated  from  the  two  halves  of  the  ventral  arch, 
which  meet  in  the  middle  line,  and  are  prolonged  into  a 
haemal  spine.  In  the  posterior  trunk  region  they  sometimes 
form  distinct  processes  diverging  from  the  two  halves  of  the 
ventral  arch ;  while  further  forward  they  may  shift  their 
attachment  so  as  to  arise  from  the  dorsal  side  of  the  two 
halves  of  the  ventral  arch  and  at  some  distance  from  their 
ends,  which  now  diverge  as  veritri- lateral  processes. 

APPENDICULAR  SKELETON. 
PECTORAL  GIRDLE. 

The  simplest  type  of  pectoral  girdle  is  found  in  Elasmo- 
branchs.  It  is  entirely  cartilaginous  and  consists  of  a  curved 
ventrally-placed  rod,  ending  dorsally  in  two  horn-like  scapular 
processes  which  are  sometimes  attached  to  the  cranium  or 
vertebral  column.  In  Rays  the  shoulder  girdle  is  very  large, 
and  has  a  distinct  suprascapular  portion  forming  a  broad  plate 
attached  to  the  neural  spines  of  the  vertebrae.  There  is  often 
a  cup-like  glenoid  cavity  for  the  articulation  of  the  limb ;  this 
cavity  is  specially  large  in  Rays  and  is  much  pierced  by  holes. 
In  Dipnoi  the  cartilaginous  girdle  still  occurs,  but  on  it  there  is 
a  deposit  of  membrane  bone  forming  the  clavicle,  inf raclavicle, 
and  supraclavicle.  These  bones,  which  with  the  exception  of 
the  clavicle,  are  unknown  in  higher  vertebrates,  are  better 
developed  in  Ganoids,  and  best  of  all  in  Teleosteans.  They 
are  connected  by  the  supra- temporal  with  the  epi-otic  and 
opisthotic  regions  of  the  cranium.  Owing  to  this  development 
of  dermal  bone,  the  original  cartilaginous  arch  becomes  much 
reduced,  but  ossifications  representing  the  scapula  and  cora- 
coid  occur  in  bony  Ganoids  and  Teleosteans. 


THE    SKELETON    IN    FISHES.      PAIRED    FINS.  127 

PELVIC  GIRDLE. 

In  Elasmobranchs  the  pelvic  girdle  consists  of  a  short 
ventral  rod  of  cartilage  representing  the  ischium  and  pubis, 
which  does  not  send  up  dorsal  iliac  processes.  In  Ohimaera 
the  pelvic  girdle  has  a  flattened  pointed  iliac  portion,  and 
ventrally  an  unpaired  movable  cartilaginous  plate  which 
bears  hooks  and  is  supposed  to  be  copulatory  in  function. 
Claspers  of  the  usual  type  are  present  as  well.  The  Dipnoi 
have  a  primitive  kind  of  pelvis  in  the  form  of  a  cartilaginous 
plate  lying  in  the  mid  ventral  line  and  drawn  out  into  three 
horns  anteriorly.  In  Ganoids  the  pelvis  has  almost  entirely 
disappeared,  though  small  cartilaginous  vestiges  of  it  remain 
in  Polypterus.  In  Teleosteans  even  these  vestiges  are  gone, 
and  in  these  fish  and  Ganoids  the  place  of  the  pelvis  is  taken 
by  the  enlarged  basi-pterygia  (meta-pterygia)  of  the  fins. 

PAIRED  FINS1. 

As  regards  the  origin  of  the  limbs  or  paired  fins  of  fishes 
there  are  two  principal  views.  One  view,  that  of  Gegenbaur, 
considers  that  limbs  and  their  girdles  are  derived  from  visceral 
arches  which  have  migrated  backwards.  The  other  view,  which 
probably  now  has  the  greater  number  of  supporters,  considers 
that  the  paired  fins  of  fishes  are  of  essentially  the  same  nature 
as  the  median  fins. 

According  to  Gegenbaur's  view2  the  archipterygium  of 
Ceratodus  (fig.  20)  represents  the  lowest  type  of  fin  ;  it  con- 
sists of  a  central  cartilaginous  axis  bearing  a  large  number  of 
radialia.  The  dorsal  or  pre- axial  radialia  are  more  numerous 
than  the  ventral  or  postaxial,  and  at  the  margin  of  the  fin3  the 

1  A.  Smith  Woodward,  Nat.  Sci.  vol.  1. 1892,  p.  28.    Further  references 
are  here  given  on  the  literature  of  the  subject. 

2  C.  Gegenbaur,  Ueber  das  Archipterygium,  Jena  Zeitschr.  der  Wirbel- 
thiere,  2e  Heft,  1873,  vol.  7,  and  MorphoL  Jahrb.  xxn.  1894,  p.  119. 

3  The  fins  of  Ceratodus  are  very  variable,  no  two  being  exactly  alike. 
Sometimes   even   the  main  axis  bifurcates.     See  W.  A.  Haswell,  Linn. 
Soc.  N.  S.  Wales,  vol.  vn.  1882. 


128 


THE  VERTEBRATE  SKELETON. 


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THE   SKELETON   IN    FISHES.      PAIRED   FINS.  129 

cartilaginous  endoskeletal  radialia  are  replaced  by  horny  exo- 
skeletal  fin-rays. 

It  is  impossible  here  to  give  a  full  discussion  of  the  rival 
views,  but  some  of  the  points  which  support  Gegenbaur's  view 
may  be  mentioned.  The  fact  that  migration  of  visceral  arches 
has  to  be  assumed  is  no  difficulty,  as  it  is  obvious  that 
migration  in  the  opposite  direction  has  taken  place  in  many 
Teleosteans  such  as  the  Cod,  whose  pelvic  fins  are  attached 
to  the  throat  in  front  of  the  pectorals.  If  migration  did  take 
place,  the  pelvic  fins  being  older  than  the  pectoral  should  be 
the  more  modified,  and  this  is  the  case.  Again,  if  the  pectoral 
girdle  is  a  modified  branchial  arch,  it  must  at  some  period 
have  carried  a  gill,  and  in  Protopterus  it  does  bear  a  vestigial 
gill. 

According  to  the  view  more  prevalent  at  the  present  time, 
the  paired  fins  have  been  derived  from  two  continuous  folds 
of  skin  and  their  skeletal  supports  running  forward  from  the 
anal  region  along  the  sides  of  the  body,  their  character  being 
similar  to  the  fold  that  gave  rise  to  the  median  fins.  In 
support  of  this  view  it  may  be  argued  that  the  paired  and 
unpaired  fins  are  often  identical  in  structure,  and  that  some 
Elasmobranch  embryos  do  show  a  ridge  running  between  the 
pectoral  and  pelvic  fins.  Then  from  this  continuous  fold  two 
pairs  of  smaller  folds  may  have  been  specialised  off,  and  in 
each  a  number  of  cartilaginous  radialia  may  have  been  de- 
veloped. The  fin  of  Cladoselache  from  the  Carboniferous  of 
Ohio  apparently  illustrates  this  condition.  It  consists  of 
certain  basal  pieces  which  do  not  project  beyond  the  body 
wall  and  bear  a  number  of  unsegmented  cartilaginous  radialia, 
which  show  crowding  together  and  are  sometimes  bifurcated 
distally ;  they  extend  throughout  the  whole  fin  from  the  body 
wall  to  the  margin.  From  this  fin  the  archipterygium  might 
be  easily  derived  by  the  enlargement  of  one  of  the  middle 
radialia  and  the  segmentation  and  partial  fusion  of  them  all. 
Whether  the  archipterygium  be  a  primitive  or  secondary 

R.  9 


130          THE  VERTEBRATE  SKELETON. 

type  of  fin,  when  it  is  once  reached  it  is  easy  to  derive  all  the 
other  types  from  it.  The  fins  of  the  other  living  Dipnoi, — 
Protopterus  and  Lepidosiren — are  simply  archipterygia  from 
which  the  radialia  have  almost  or  completely  disappeared, 
leaving  only  the  segmented  axes.  Archipterygia  too  are  found 
in  the  pectoral  fins  of  the  Ichthyotomi,  but  the  postaxial 
radialia  are  much  reduced. 

The  ichthyopterygium,  or  type  of  fin,  characteristic  of 
many  modern  Elasmobranchs  such  as  Scyllium,  may  have  been 
derived  from  the  archipterygium  by  the  gradual  reduction  of 
the  rays  on  the  postaxial  side  of  the  axis  and  their  condensation 
on  the  pre-axial  side.  The  Ichthyotomi  such  as  Xenacanthus 
show  one  stage  in  the  reduction  of  the  post-axial  rays,  and  a 
further  stage  is  seen  in  the  Notidanidae  and  some  other  sharks 
like  Scymnus  and  Acanthias,  in  which  a  few  postaxial  rays 
still  remain.  The  condensation  of  the  pre-axial  rays  when 
further  continued  leads  to  one  of  the  rays  getting  an  attach- 
ment to  the  girdle.  Thus  the  fin  comes  to  articulate  with  the 
girdle  by  two  basalia  or  basal  pieces ;  a  third  attachment  is 
formed  in  the  same  way  and  the  three  basalia  are  called  re- 
spectively pro-,  meso-,  and  meta-pterygia.  By  some  authors  the 
meta-pterygium  and  by  others  the  meso-pterygium  is  regarded 
as  homologous  with  the  axis  of  the  archipterygium. 

The  pectoral  fins  of  Elasmobranchs  vary  very  much  in 
their  mode  of  attachment.  In  some  of  the  sharks,  including 
the  Notidanidae  and  Scy Ilium,  all  three  basalia  articulate  with 
the  pectoral  girdle,  while  in  others  such  as  Cestracion  the 
meta-pterygium  is  excluded.  In  Rays  the  pro-pterygium  and 
the  meta-pterygium  are  long  and  narrow  and  diverge  much 
from  one  another;  other  basalia  work  their  way  in  between 
the  meso-pterygium  and  meta-pterygium,  and  come  to  arti- 
culate with  the  pectoral  girdle.  Sometimes  they  fuse  and 
form  a  second  meso-pterygium.  The  radialia  are  greatly 
elongated  and  are  segmented. 

In  Chimaera  all  three  basalia  are  present,  but  the  meso- 


THE    SKELETON    IN    FISHES.      PAIRED    FINS.          131 

pterygium  is  shifted  and  does  not  articulate  with  the  pectoral 
girdle J. 

In  Acipenser  and  Polyodon  the  pectoral  fin  is  built  on  the 
same  type  as  in  Elasmobranchs,  but  becomes  modified  from  the 
fact  that  the  pro-pterygium  is  replaced  by  dermal  bone  which 
forms  a  large  marginal  ray.  Extra  meso-pterygia  are  formed 
in  the  same  way  as  in  Rays. 

In  Polypterus  the  pro-  and  meta-pterygia  have  ossified 
while  the  meso-pterygium  remains  chiefly  cartilaginous;  the 
fin-rays  are  also  chiefly  ossified. 

In  Amia,  Lepidosteus,  and  certain  Teleosteans  like  Salmo, 
not  only  the  pro-pterygium  but  the  meso-pterygium  is  almost 
suppressed  by  the  marginal  ray. 

In  the  great  majority  of  Teleosteans  a  still  further  stage  is 
reached,  the  endoskeletal  elements,  the  basalia  and  radialia 
are  almost  entirely  suppressed  and  the  fin  comes  to  consist 
entirely  of  ossified  fin-rays  of  dermal  origin. 

In  some  Teleosteans — Exocaetus,  a  herring,  and  Dactylo- 
pterus,  a  gurnard — the  pectoral  fins  are  so  enormously  developed 
that  by  means  of  them  the  fish  is  able  to  fly  through  the  air 
for  considerable  distances.  The  skeleton  of  these  great  fins  is 
almost  entirely  composed  of  dermal  bone. 

PELVIC  FIN. 

The  pelvic  fin  is  almost  always  further  removed  from  the 
archipterygial  condition,  and  is  in  general  more  modified  than  is 
the  pectoral.  Thus  in  the  Ichthyotomi,  while  the  pectoral  fins 
are  archipterygia  similar  to  those  of  Ceratodus,  the  pelvic  fins 
consist  of  an  axis  bearing  rays  on  the  postaxial  side  only,  and 
prolonged  distally  into  a  clasper.  In  Dipnoi  however  the 
pelvic  fins  are  very  similar  to  the  pectoral.  In  Elasmobranchs 
the  meso-pterygium  is  missing,  the  pro-pterygium  is  small  or 
absent,  and  the  fin  is  mainly  composed  of  the  meta-pterygium 

1  Some  of  these  views  with  regard  to  the  homologies  of  the  parts  of 
the  fins  are  not  accepted  by  all  anatomists. 

9—2 


132          THE  VERTEBRATE  SKELETON. 

(generally  called  basi-pterygium)  and  its  radialia.  The  males 
in  Elasmobranchii  and  Holocephali  have  the  distal  end  of  the 
metapterygium  prolonged  into  a  clasper. 

In  Ganoids  and  in  Teleosteans  the  loss  of  the  pelvic  girdle 
causes  the  pelvic  fin  to  be  still  further  removed  from  the 
primitive  state.  There  is  always  a  large  basi-pterygium  which 
lies  imbedded  in  the  muscles  and  meets  its  fellow  at  its  proximal 
end.  In  Cartilaginous  Ganoids  it  has  a  secondary  segmenta- 
tion. Its  relation  to  its  fellow  is  subject  to  much  variation 
in  Teleosteans,  sometimes  as  in  the  Perch  the  two  are  in 
contact  throughout,  sometimes  as  in  the  Salmon  they  meet 
distally  as  well  as  proximally,  but  are  elsewhere  separated  by 
a  space,  sometimes  as  in  the  Pike  and  Bony  Ganoids  they 
diverge  widely.  The  radialia  are  articulated  to  the  basi- 
pterygium.  In  Cartilaginous  Ganoids  and  Polypterus  they 
are  well  developed,  in  other  Ganoids  and  in  Teleosteans  they 
are  in  the  main  replaced  by  dermal  fin-rays. 

In  some  Teleosteans  such  as  the  Cod  the  pelvic  fins  have 
migrated  from  their  usual  position  and  come  to  be  attached 
to  the  throat  in  front  of  the  pectoral  fins.  Fish  with  this 
arrangement  are  grouped  together  as  jugulares. 


CHAPTER   IX. 
CLASS  II.     AMPHIBIA1. 

AMPHIBIA  differ  markedly  from  Pisces  in  the  fact  that 
in  the  more  abundant  and  familiar  forms  the  skin  is  naked, 
and  that  when  the  integument  is  prolonged  into  median  fins 
they  are  devoid  of  fin-rays.  The  notochord  may  persist,  but 
bony  vertebral  centra  are  always  developed.  These  are  some- 
times biconcave,  sometimes  procoelous,  sometimes  opistho- 
coelous.  There  is  only  one  sacral  vertebra,  except  in  rare 
cases.  The  cartilaginous  cranium  persists  to  a  considerable 
extent  but  is  more  or  less  replaced  by  cartilage  bone,  and 
overlain  by  membrane  bone.  The  basi-occipital  is  not  com- 
pletely ossified,  and  the  skull  articulates  with  the  vertebral 
column  by  means  of  two  occipital  condyles  formed  by  the 
exoccipitals. 

There  is  a  large  parasphenoid,  but  there  are  no  ossifications 
in  the  basisphenoidal,  presphenoidal,  and  alisphenoidal  re- 
gions. In  most  cases  the  epi-otics  and  opisthotics  are  ossified 
continuously  with  the  exoccipitals. 

The  palato-pterygo-quadrate  bar  is  firmly  united  to  the 
cranium,  so  the  skull  is  autostylic.  The  palatines  and 
pterygoids  are  membrane  bones.  Teeth  are  nearly  always 
borne  on  the  vomers  and  commonly  on  the  maxillae  and 

1  T.  H.  Huxley,  Amphibia  (Encyclopedia  Britannica). 


134          THE  VERTEBRATE  SKELETON. 

premaxillae.  There  are  no  sternal  ribs,  and  the  sternum  is 
very  intimately  related  to  the  pectoral  girdle.  There  are  no 
obturator  foramina.  The  limbs  are  as  in  the  higher  verte- 
brata,  divisible  into  upper  arm,  fore-arm,  and  manus  (wrist 
and  hand),  and  into  thigh,  shin,  and  pes  (ankle  and  foot) 
respectively.  The  posterior  limb  is,  as  a  rule,  pentedactylate, 
but  in  nearly  every  case  the  pollex  is  vestigial  or  absent. 

Order  1.     URODELA1. 

The  Urodela  are  elongated  animals  with  a  naked  skin,  a 
persistent  tail,  and  generally  four  short  limbs. 

The  vertebral  centra  are  opisthocoelous  or  biconcave,  and 
there  are  numerous  precaudal  vertebrae.  Portions  of  the 
notochord  commonly  persist  in  the  intervertebral  spaces.  In 
the  skull  there  is  no  sphenethmoid  forming  a  ring  encircling 
the  anterior  end  of  the  brain,  its  place  being  in  many  cases 
partly  taken  by  a  pair  of  orbitosphenoids.  There  is  no 
quadra tojugal,  and  the  quadrate  is  more  or  less  ossified.  The 
mandible  has  a  distinct  splenial,  and  the  articular  is  ossified. 

There  is  no  definite  tympanic  cavity.  The  hyoid  apparatus 
is  throughout  life  connected  to  the  quadrate  by  ligament,  and 
a  large  basilingual  plate  does  not  occur.  The  ribs  are  short 
structures  with  bifurcated  proximal  ends.  In  the  pelvis  the 
pubis  remains  cartilaginous,  and  there  is  a  bifid  cartilaginous 
epipubis.  The  bones  of  the  fore-arm  and  shin  remain  distinct, 
and  the  manus  never  has  more  than  four  digits. 

Suborder  (1).     ICHTHYOIDEA. 

The  vertebrae  are  amphicoelous,  but  the  notochord  re- 
mains but  little  constricted  throughout  the  whole  length  of 
the  vertebral  column.  Three  or  four  branchial  arches  nearly 
always  persist  in  the  adult.  The  cartilages  of  the  carpus 
and  tarsus  remain  unossified. 

1  See  E.  Wiedersheim,  Morpkol.  Jahrb.  Bd.  in.  1877,  p.  459. 


AMPHIBIA.      URODELA.  135 

The  Ichthyoidea  may  be  subdivided  again  into  two 
groups  : — 

A.  Perennibranchiata,  whose  chief  distinguishing  skeletal 
characters  are  that  the  skull  is  elongated,  the  premaxillae  are 
not  ankylosed,  the  maxillae  are  vestigial  or  absent ;  there  are 
sometimes  no  nasals,  and  the  palatines  bear  teeth ; 

e.g.  Siren,  Proteus,  Menobranchus. 

B.  Derotremata,  whose  chief  distinguishing  skeletal  cha- 
racters are  that  there  are  large  maxillae  and  nasals  \  teeth  are 
borne  by  both  maxillae  and  premaxillae ;  there  are  no  pala- 
tines ;  and  both  pectoral  and  pelvic  limbs  are  always  present ; 

e.g.   Amphiuma,  Megalobatrachus,  Cryptobranclm-s. 

Suborder  (2).     SALAMANDRINA. 

The  vertebrae  are  opisthocoelous.  The  skull  is  broad,  and 
teeth  are  borne  by  both  premaxillae  and  dentaries.  Nasal 
bones  are  present.  The  remains  of  only  two  branchial  arches 
are  found  in  the  adult.  The  carpus  and  tarsus  are  more  or 
less  ossified. 

This  suborder  includes  the  Newts  (Molge),  Salamanders 
(Salamandra),  and  Amblystoma. 

Order    2.       LABYRINTHODONTIA1. 

These  are  extinct  Amphibia  with  a  greatly  developed 
dermal  exoskeleton,  which  is  generally  limited  to  the  ventral 
surface.  The  body  and  tail  are  long  and  in  some  cases  limbs 
are  absent.  The  teeth  are  pointed  and  often  have  the  dentine 
remarkably  folded.  The  vertebrae  are  amphicoelous,  and  are 
generally  well  ossified.  The  skull  is  very  solid,  and  has  a 
greatly-developed  secondary  roof  which  hides  the  true  cranium 

1  See  A.  Fritsch,  Fauna  der  Gaskohle,  Prague,  1883-85-86,  also  writings 
of  Cope,  Credner,  Huxley,  H.  v.  Meyer,  Miall. 


136          THE  VERTEBRATE  SKELETON. 

and  is  very  little  broken  up  by  fossae.  Paired  dermal  supra- 
occipitals  are  found,  and  there  is  an  interparietal  foramen. 
The  epi-otics  and  opisthotics  form  a  pair  of  bones  distinct  from 
the  exoccipitals.  Four  simple  limbs  of  moderate  length  are 
generally  present,  and  in  some  cases  all  four  limbs  are  pente- 
dactylate.  Among  the  better  known  genera  of  Labyrinthodonts 
are  Mastodonsaurus,  Nyrania,  and  Archegosaurus. 

Order  3.     GYMNOPHIONAJ. 

These  animals  form  a  group  of  abnormal  worm-like  Am- 
phibia having  an  exoskeleton  in  the  form  of  subcutaneous 
scales  arranged  in  rings.  The  vertebrae  are  biconcave  and  are 
very  numerous;  very  few  however  belong  to  the  tail.  The 
skull  has  a  complete  secondary  bony  roof,  the  mandible 
bears  teeth  and  has  an  enormous  backward  projection  of  the 
angular.  The  hyoid  arch  has  very  slender  cornua  and  no 
distinct  body,  it  is  attached  neither  to  the  cranium  nor  to 
the  suspensorium.  The  ribs  are  very  long  and  there  are  no 
limbs  or  limb  girdles, 

Order  4.     ANURA. 

These  are  tailless  Amphibia,  which  except  in  a  few  in- 
stances, are  devoid  of  an  exoskeleton.  The  vertebrae  are  as 
a  rule  procoelous,  and  are  very  few  in  number.  The  post- 
sacral  part  of  the  spinal  column  ossifies  continuously,  forming 
an  unsegmented  cylindrical  rod,  the  urostyle.  Remains  of  the 
notochord  persist,  lying  vertebrally,  i.e.  enclosed  within  the 
centra  of  the  several  vertebrae,  and  not  as  in  Urodela  lying 
between  one  vertebra  and  the  next.  The  skull  is  very  short 
and  wide.  The  mandible  is  almost  always,  if  not  invariably, 
toothless. 

The  f  rentals  and  parietals  on  each  side  are  united  so  as  to 
form  a  pair  of  fronto-parietals,  and  a  girdle-like  sphenethmoid 
is  present. 

1  See  R.  Wiedersheim,  Anatomie  der  Gymnophionen,  Jena,  1879. 


AMPHIBIA.      ANURA.  137 

The  quadrate  is  not  generally  ossified.  A  pre-dentary  or 
mento-meckelian  bone  is  commonly  present  in  the  mandible, 
and  a  single  bone  represents  the  angular  and  splenial.  The 
branchial  arches  are  much  reduced  in  the  adult,  and  the  distal 
ends  of  the  cornua  unite  to  form  a  flat  basilingual  plate  of  a 
comparatively  large  size. 

Ribs  are  very  little  developed.  Clavicles  are  present. 
The  ilia  are  very  greatly  elongated.  The  anterior  limb  has 
four  well-developed  digits  and  a  vestigial  pollex,  and  is  of 
moderate  length ;  the  radius  and  ulna  have  fused.  The 
posterior  limb  is  greatly  elongated  and  is  pentedactylate ;  the 
tibia  and  fibula  are  fused,  while  the  calcaneura  and  astragalus 
are  greatly  elongated,  and  it  is  largely  owing  to  them  that 
the  length  of  the  limb  is  so  great.  The  group  includes  the 
Frogs  and  Toads,  the  predominant  Amphibia  of  the  present 
time. 


CHAPTER  X. 
THE    SKELETON    OF   THE    NEWT   (Molge  cristata}. 

I.  EXOSKELETON. 

The  skin  of  the  Newt  is  quite  devoid  of  any  exoskeletal 
structures.  The  only  exoskeletal  structures  that  the  animal 
possesses  are  the  teeth,  and  these  are  most  conveniently  de- 
scribed with  the  endoskeleton. 

II.  ENDOSKELETON. 

The  endoskeleton  of  the  Newt,  though  ossified  to  a  con- 
siderable extent,  is  more  cartilaginous  than  is  that  of  the  frog. 
It  is  divisible  into  an  axial  portion  including  the  vertebral 
column,  skull,  ribs,  and  sternum,  and  an  appendicular  por- 
tion including  the  skeleton  of  the  limbs  and  their  girdles. 

1.     THE  AXIAL  SKELETON. 

A.     THE  VERTEBRAL  COLUMN. 

This  consists  of  about  fifty  vertebrae  arranged  in  a  regular 
continuous  series.  The  first  vertebra  differs  a  good  deal  from 
any  of  the  others ;  the  seventeenth  or  sacral  vertebra  and  the 
eighteenth  or  first  caudal  also  present  peculiarities  of  their 
own.  The  remaining  vertebrae  are  divided  by  the  sacrum 
into  an  anterior  series  of  trunk  vertebrae  whicli  bear  fairly 


THE  SKELETON  OF  THE  NEWT.   VERTEBRAE.   139 

large  ribs,  and  a  posterior  series  of  caudal  vertebrae,  all  of 
which  except  the  first  few  are  ribless. 

THE    TRUNK    VERTEBRAE. 

Any  vertebra  from  the  second  to  the  sixteenth  may  be 
taken  as  a  type  of  the  trunk  vertebrae. 

The  general  form  is  elongated  and  somewhat  hour-glass 
shaped,  and  the  centra  are  convex  in  front  and  concave 
behind ;  an  opisthocoelous  condition  such  as  this  is  quite  ex- 
ceptional in  Anura.  The  note-chord  may  persist  interverte- 
brally1,  but  in  the  centre  of  each  vertebra  it  becomes  greatly 
constricted  or  altogether  obliterated,  and  replaced  by  marrow. 
The  superficial  portion  of  the  centrum  is  ossified,  while  the 
articular  surfaces  are  cartilaginous.  The  neural  arches  are 
low  and  articulate  together  by  means  of  zygapophyses  borne 
on  short  diverging  processes.  The  anterior  zygapophyses  look 
upwards,  the  posterior  downwards.  Each  neural  arch  is  drawn 
out  dorsally  into  a  very  slight  cartilaginous  neural  spine. 

On  each  centrum,  at  a  little  behind  the  middle  line,  there 
arise  a  pair  of  short  backwardly-directed  transverse  pro- 
cesses; each  of  which  becomes  divided  into  two  slightly 
divergent  portions,  a  dorsal  portion  which  meets  the  tubercular 
process  of  the  rib  and  is  derived  from  the  neural  arch,  and  a 
ventral  portion  which  meets  the  capitular  process  of  the  rib 
and  is  derived  from  the  ventral  or  haemal  arch.  The  division 
between  these  two  parts  of  the  transverse  processes  can  be 
traced  back  as  far  as  the  sacrum. 

The  first  vertebra  as  already  mentioned  differs  much 
from  all  the  others.  It  has  no  ribs,  and  presents  anteriorly 
two  slightly  divergent  concave  surfaces  which  articulate  with 
the  occipital  condyles  of  the  skull.  Between  these  surfaces 
the  dorsal  portion  of  the  anterior  face  of  the  centrum  is 
drawn  out  into  a  prominent  odontoid  process,  the  occur- 
rence of  which  renders  it  probable  that  the  first  vertebra  of 

1  i.e.  between  one  vertebra  and  the  next. 


140          THE  VERTEBRATE  SKELETON. 

the  newt  is  really  the  axis,  and  that  the  atlas  with  the  excep- 
tion of  the  odontoid  process  has  become  fused  with  the  skull. 
The  sacral  vertebra  or  sacrum,  differs  from  the  vertebrae 
immediately  in  front  of  it  only  in  the  fact  that  its  transverse 
processes  are  stouter  and  more  obviously  divided  into  dorsal 
and  ventral  portions. 

THE    CAUDAL    VERTEBRAE. 

The  caudal  vertebrae  are  about  twenty-four  in  number. 
The  anterior  ones  have  hour-glass  shaped  centra,  and  short 
backwardly-directed  transverse  processes.  The  middle  and 
posterior  ones  have  rather  shorter  centra,  and  are  without 
transverse  processes.  The  neural  arches  resemble  those  of  the 
trunk  vertebrae,  but  each  is  drawn  out  into  a  rather  high 
cartilaginous  neural  spine  abruptly  truncated  anteriorly.  All 
the  caudal  vertebrae  except  the  first  have  also  a  haemal  arch, 
which  is  very  similar  to  the  neural  arch,  and  is  drawn  out 
into  a  haemal  spine  quite  similar  to  the  neural  spine.  Both 
neural  and  haemal  arches  are  ossified  continuously  with  the 
centra. 

B.     THE  SKULL. 

The  skull  of  the  newt  is  divisible  into  three  principal 
parts  : — 

(1)  an  axial  part,  the  cranium  proper,  which  encloses 
the  brain  and  to  which 

(2)  the  capsules  of  the  auditory  and  olfactory  sense 
organs  are  fused ; 

(3)  the  skeleton  of  the  jaws  and  hyoid  apparatus. 
The  skull  is  much  flattened  and  expanded,  though  not  so  much 
as  in  the  frog. 

(1)       THE    CRANIUM    PROPER. 

The  cranium  proper  or  brain  case  is  an  unsegmented 
tube  which  remains  partly  cartilaginous,  and  is  partly  con- 
verted into  cartilage  bone,  partly  sheathed  by  membrane  bone. 
The  roof  and  floor  of  the  cartilaginous  cranium  are,  as  is 


THE  SKELETON  OF  THE  NEWT.   THE  CRANIUM.  141 

the  case  also  in  the  frog,  pierced  by  holes  or  fontanelles,  and 
these  are  so  large  that  the  main  part  of  the  roof  and  floor 
comes  to  be  formed  by  membrane  bone. 

Two  pairs  of  large  ossifications  take  place  in  the  cranial 
walls.  Of  these  the  more  posterior  on  each  side  represents 
the  exoccipital  and  all  three  periotic  bones.  It  bears  a 
small  convex  patch  of  cartilage  for  articulation  with  the  atlas, 
and  with  its  fellow  forms  the  boundary  of  the  foramen  magnum. 

Two  foramina  pierce  the  exoccipital  just  in  front  of  the 
occipital  condyle  and  transmit  respectively  the  glossopharyngeal 
and  pneumogastric  (fig.  21,  X)  nerves.  Lying  laterally  to 
these  nerve  openings  is  seen  a  patch  of  cartilage,  the  stapes, 
which  is  homologous  with  the  stapes  or  proximal  element  of 
the  columellar  chain  in  the  frog.  Further  forward  in  front  of 
the  stapes  is  the  small  opening  for  the  exit  of  the  facial  nerve, 
and  seen  in  a  lateral  view  close  to  the  orbitosphenoid,  that 
for  the  trigeminal  (fig.  21,  C,  5). 

In  front  of  these  large  bones  the  lateral  parts  of  the 
cranial  walls  remain  cartilaginous  for  a  short  distance,  and 
then  there  follow  two  elongated  bones,  the  orbitosphenoids 
(tig.  21,  B  and  C,  11),  pierced  by  the  foramina  for  the  exit 
of  the  optic  nerves.  These  bones  partly  correspond  to  the 
sphenethmoid  of  the  frog. 

The  membrane  bones  connected  with  the  cranium  are  the 
parietals,  frontals  and  prefronto-lachrymals  on  the  dorsal 
surface,  and  the  parasphenoid  on  the  ventral  surface. 

The  parietals  (fig.  21,  A  and  C,  6)  roof  over  the  posterior 
part  of  the  great  dorsal  fontanelle  and  overlap  the  exoccipito- 
periotics.  They  meet  one  another  along  a  sinuous  suture  in 
the  middle  line,  as  do  also  the  frontals  which  overlap  them 
in  front.  The  frontals  and  parietals  both  extend  for  a  short 
distance  down  the  sides  of  the  cranium  and  meet  the  orbito- 
sphenoids. The  prefronto-lachrymals  (fig.  21,  A  and  C,  7) 
connect  the  frontals  with  the  maxillae. 

On  the  ventral  surface  is  the  large  parasphenoid  (fig.  21, 


142 


THE  VERTEBRATE  SKELETON. 

22 


FlG.    21.      A   DORSAL,    B    VENTRAL,    AND    C    LATERAL   VIEWS    OF   THE    SKULL 

OF  A  NEWT  (Molge  cristata)  x  2^  (after  PARKER). 

The  cartilage  is  dotted,  the  cartilage  bones  are  marked  with  dots  and 
dashes,  the  membrane  bones  are  left  white. 


1.  premaxilla. 

2.  anterior  nares. 

3.  posterior  nares. 

4.  nasal. 

5.  frontal. 

6.  parietal. 

7.  prefronto-lachrymal. 

8.  maxilla. 

9.  vomero-palatine. 

10.  parasphenoid. 

11.  orbitosphenoid. 

12.  pterygoid. 

13.  squamosal. 


14.  pro-otic  region  of  exoccipito- 

periotic. 

15.  quadrate. 

16.  quadrate  cartilage. 

17.  exoccipital    region  of  exoc- 

cipito-periotic. 

18.  articular. 

19.  articular  cartilage. 

20.  dentary. 

21.  splenial. 

22.  middle  narial  passage. 

II.  V.  VII.  IX.  X.  foramina  for 
the  exit  of  cranial  nerves. 


THE   SKELETON   OF   THE   NEWT.      SENSE   CAPSULES.      143 

B,   10),    which    is   widest    behind    and   overlapped   anteriorly 
by  the  vomero-palatines. 

(2)  THE  SENSE  CAPSULES. 

The  auditory  capsules  become  almost  completely  ossified 
continuously  with  the  exoccipitals ;  they  have  been  already 
described. 

The  nasal  capsules  are  large  and  quite  unossified  though 
they  are  overlain  by  membrane  bone.  They  appear  on  the 
dorsal  surface  between  the  anterior  nares  and  the  nasal  process 
of  the  premaxillae.  They  enclose  the  nasal  organs,  bound 
the  inner  side  of  the  anterior  narial  opening,  and  are  con- 
nected with  one  another  posteriorly  by  a  cartilaginous  area. 

Developed  in  connection  with  the  nasal  capsules  are  a  pair 
of  rather  large  nasals  (fig.  21,  A  and  C,  4),  which  lie  on  the 
dorsal  surface  immediately  in  front  of  the  frontals.  Each 
forms  part  of  the  posterior  boundary  of  one  of  the  anterior 
nares,  and  the  two  are  separated  from  one  another  in 
the  middle  line  by  the  nasal  process  of  the  premaxillae 
(fig.  21,  A,  1),  and  the  opening  of  the  middle  narial  passage 
(tig.  21,  A  and  B,  22),  which  passes  right  through  the  skull. 

On  the  ventral  surface  of  the  skull  and  forming  the  greater 
part  of  the  boundary  of  the  posterior  nares  are  two  large 
bones,  the  vomero-palatines  (fig.  21,  B  and  C,  9).  Each  consists 
of  a  wide  anterior  portion,  partly  separated  from  its  fellow  in 
the  middle  line  by  the  ventral  opening  of  the  middle  narial 
passage,  and  of  a  long  pointed  posterior  portion  which  is 
separated  from  its  fellow  by  the  parasphenoid,  and  bears  a  row 
of  small  pointed  teeth  formed  of  dentine  capped  with  enamel. 

(3)  THE  JAWS. 

The  upper  jaw  of  the  newt  is  a  discontinuous  structure 
divided  into  two  parts,  an  anterior  part  which  consists  of 
membrane  bones,  the  maxillae  and  premaxillae,  and  a  posterior 
part  which  remains  mainly  cartilaginous. 

The  premaxillae  are  united,  forming  a  single  bone,  which  in 


144  THE  VERTEBRATE  SKELETON. 

a  ventral  view  is  seen  to  meet  the  maxillae  and  vomero- 
palatines,  and  in  a  dorsal  view  to  send  back  a  nasal  process 
(fig.  21,  A,  1)  between  the  nasals. 

The  maxillae  are  large  bones,  each  terminating  in  a  point 
posteriorly.  A  single  row  of  teeth  similar  to  those  on  the 
vomero-palatines  runs  along  the  outer  margin  of  the  maxillae 
and  prem  axillae. 

The  posterior  part  of  the  upper  jaw  forms  a  mass  of 
cartilage  which  extends  forwards  towards  the  maxilla  as  a 
long  pointed  process  whose  ventral  surface  and  sides  are  over- 
lapped by  a  membrane  bone,  the  pterygoid  (fig.  21,  12). 

The  suspensorial  bones  include  the  quadrate  and  squa- 
mosal.  The  quadrate  (fig.  21,  15)  which  forms  the  true 
suspensorium  is  directed  forwards  and  outwards,  and  is 
terminated  by  a  patch  of  cartilage  with  which  the  mandible 
articulates. 

The  lower  jaw  or  mandible  remains  partly  cartilaginous, 
while  its  ossifications  include  two  membrane  bones  and  one 
cartilage  bone.  The  cartilage  bone  is  the  articular  (fig.  21,  C, 
18),  it  forms  the  posterior  part  of  the  ramus,  extends  forwards 
for  some  distance  along  its  inner  side,  and  is  terminated 
posteriorly  by  a  patch  of  cartilage  which  articulates  with  the 
quadrate.  The  dentary  (fig.  21,  C,  20)  is  a  large  bone  which  forms 
the  anterior  part  and  nearly  all  the  outer  half  of  each  ramus, 
and  bears  teeth  similar  to  those  of  the  upper  jaw.  Attached 
to  its  inner  face  is  a  long  slender  splenial  (fig.  21,  C,  21). 

THE  HYOID  APPARATUS. 

This  consists  of  the  hyoid  arch  and  part  of  the  first  two 
branchial  arches. 

The  hyoid  arch  (fig.  21,  A,  2)  consists  of  a  pair  of  cornua, 
each  of  which  is  divided  into  two  halves.  The  dorsal  half 
forming  the  cerato-hyal  is  mainly  ossified  though  tipped  with 
cartilage,  and  is  connected  by  ligament  with  the  suspensorium. 
The  ventral  half  (hypo-hyal)  is  cartilaginous,  and  is  connected 
with  the  basi-branchial. 


THE    SKELETON    OF   THE    NEWT.      RIBS  AND   STERNUM.    145 

The  branchial  arches  consist  of  a  median  piece,  the 
basi-branchial,  which  is  ossified  in  the  centre  and  cartila- 
ginous at  either  end,  and  of  two  pairs  of  cerato-branchials 
which  are  attached  to  the  cartilaginous  part  (fig.  29,  A,  8) 
of  the  basi-branchial.  The  first  cera to-branchial  is  chiefly 
ossified,  the  second  (fig.  29,  A,  4)  is  a  good  deal  smaller  and 
is  cartilaginous.  Both  are  united  dorsally  to  a  single  epi- 
branchial,  which  is  terminated  by  a  small  cartilaginous  area 
at  the  free  end  but  is  elsewhere  well  ossified. 

C.  THE  RIBS. 

The  ribs  are  short  imperfectly  ossified  structures,  bifid 
at  their  proximal  end  where  they  articulate  with  the  trans- 
verse processes,  and  tipped  both  proximally  and  distally  with 
cartilage.  The  dorsal  portion  of  the  proximal  end  corresponds 
to  the  tuberculum  of  the  ribs  of  higher  animals,  and  the 
ventral  portion  to  the  capitiilum.  Some  of  the  anterior  ribs 
have  a  step-like  notch  on  their  dorsal  surfaces. 

The  second  to  twelfth  ribs  are  fairly  equal  in  size,  but 
further  back  they  decrease  slightly.  The  ribs  which  connect 
the  sacral  vertebrae  with  the  ilia  are  however  large.  The  short 
ribs  borne  on  the  anterior  caudal  vertebrae  are  cartilaginous. 

D.  THE  STERNUM. 

The  sternum  (fig.  22,  A,  6)  is  a  rather  broad  plate  of 
cartilage,  drawn  out  posteriorly  into  a  median  process  marked 
by  a  prominent  ridge.  On  its  antero-lateral  margins  it  bears 
surfaces  for  articulation  with  the  pectoral  girdle. 

2.     THE  APPENDICULAR  SKELETON. 

A.     THE  PECTORAL  GIRDLE. 

This  is  of  a  very  simple  character,  and  remains  throughout 
life  in  an  imperfectly  ossified  condition.  It  consists  of  a 
dorsal  scapular  portion,  and  a  ventral  coracoid  portion 
partially  divided  into  an  anterior  part,  the  precoracoid,  and 
a  posterior  part,  the  coracoid. 

R.  10 


146 


THE  VERTEBRATE  SKELETON. 


The  scapular  portion  is  a  slightly  curved  oblong  plate;  its 
proximal  third  the  scapula  (fig.  22,  1)  is  ossified  and  bounds 
part  of  the  well-marked  glenoid  cavity  (fig.  22,  4) ;  its  distal 
portion  forms  a  large  oblong  cartilaginous  plate,  the  supra- 


FlG.    22.       A    VENTKAL,    AND    B     LATEKAL     VIEW     OF    THE    SHOULDER    GIRDLE 
AND    STERNUM    OF    AN    OLD    MALE    CRESTED    NEWT    (Mol(J6     CristCttd)  X  3 

(after  PARKER). 

1.  scapula.  4.  glenoid  cavity. 

2.  suprascapula.  5.  precoracoid. 

3.  coracoid.  6.  sternum. 


THE  SKELETON  OF  THE  NEWT.   ANTERIOR  LIMB.  147 

The  precoracoid  (fig.  22,  5)  forms  a  small  forwardly- 
directed  cartilaginous  plate.  The  coracoid  (fig.  22,  3)  forms 
a  much  larger  plate,  the  greater  part  of  which  is  unossified 
and  overlaps  its  fellow  in  the  middle  line,  the  two  being  over- 
lapped by  the  sternum.  Around  the  glenoid  cavity  is  an  area 
which  is  mainly  ossified  and  is  continuous  with  the  scapula. 

B.     THE  ANTERIOR  LIMB. 

This  is  divisible  into  three  parts,  the  upper  arm  or 
brachium,  the  fore-arm  or  antibrachium,  and  the  maims. 

The  upper  arm  includes  a  single  bone,  the  humerus. 

The  humerus  is  a  slender  bone  cylindrical  in  the  middle 
and  expanded  at  either  end,  the  proximal  part  forms  a 
rounded  head  which  articulates  with  the  glenoid  cavity. 
Along  the  proximal  part  of  the  anterior  or  pre-axial  surface 
runs  a  strong  deltoid  ridge.  The  proximal  part  of  the  post- 
axial  surface  also  bears  a  small  outgrowth. 

The  fore-arm  contains  two  bones,  the  radius  and  ulna,  both 
of  which  are  small  and  imperfectly  ossified  at  their  terminations. 

The  radius  (fig.  23,  B,  11)  or  pre-axial  bone  is  rather 
the  larger  of  the  two,  and  is  considerably  expanded  at  its 
proximal  end.  The  ulna  or  post  axial  bone  is  somewhat 
expanded  distally,  but  is  not  drawn  out  proximally  into  an 
olecranon  process. 

The  manus  consists  of  two  parts,  a  group  of  small  bones 
forming  the  carpus  or  wrist,  and  the  hand. 

The  carpus  is  in  a  very  simple  unmodified  condition  as 
compared  with  that  of  the  Frog.  It  consists  of  a  proximal 
row  of  two  bones  and  a  distal  row  of  four,  with  one,  the 
centrale,  interposed  between.  All  these  bones  are  small  and 
polygonal  and  are  imbedded  in  a  plate  of  cartilage. 

The  bones  of  the  proximal  row  are  a  smaller  pre-axial  bone, 
the  radiale  (fig.  23,  B,  13),  and  a  larger  postaxial  bone,  which 
represents  the  fused  ulnare  and  intermedium  of  the  very 
simple  carpus  described  on  pp.  26  and  27. 

10—2 


148 


THE  VERTEBRATE  SKELETON. 


The  four  bones  of  the  distal  row  are  respectively  car- 
palia  2,  3,  4  and  5. 

The  hand  consists  of  four  digits,  that  corresponding  to 
the  thumb  of  the  human  hand,  judging  from  the  analogy  of 
the  frog  probably  being  the  one  that  is  absent. 

Each  digit  consists  of  a  somewhat  elongated  metacarpal 
and  of  two  or  three  phalanges.  The  metacarpals  are  contracted 
in  the  middle  and  expanded  at  either  end.  They  are  connected 
with  the  carpus  by  cartilage,  and  the  articulations  between  the 
several  phalanges,  and  between  the  metacarpals  and  phalanges 
are  also  cartilaginous.  The  second,  third,  and  fifth  digits 
have  two  phalanges  apiece,  the  fourth,  which  is  the  longest, 


18- 


m 


FlG.  23.      A   RIGHT    POSTERIOR,    AND    B    RIGHT   ANTERIOR    LIMB    OF   A   NEWT 

x  1£  (Molge  cristata). 

10.  humerus. 

11.  radius. 

12.  ulna. 

13.  radiale. 

14.  intermedium  and  ulnare  fused. 

15.  centrale  of  carpus,  the  pointing 


femur. 

tibia. 

fibula. 

tibiale. 

intermedium. 

fibulare. 

centrale  of  tarsus. 

tarsale  1. 

tarsalia  4  and  5  fused. 


I.  II.  III.  IV.  V.  digits. 


line  passes  across  carpale  2. 

16.  carpale  3. 

17.  carpale  5. 


THE    SKELETON    OF   THE   NEWT.      PELVIC    GIRDLE.      149 

has  three.  The  second  metacarpal  in  the  specimen  examined 
and  figured  articulates  partly  with  carpale  2,  partly  with 
carpale  3. 

C.  THE  PELVIC  GIRDLE. 

The  pelvic  girdle  of  the  Newt  is  in  a  much  less  modified 
condition  than  is  that  of  the  Frog  (see  p.  165).  It  consists 
of  a  dorsal  element,  the  ilium,  a  posterior  ventral  element, 
the  ischium,  and  an  anterior  ventral  element,  the  pubis,  to 
which  is  attached  an  epipubis. 

The  ilium  is  a  somewhat  cylindrical  bone  which  at  its 
ventral  end  meets  the  ischium,  and  forms  part  of  the  ace- 
tabulum.  It  is  then  directed  upwards  and  slightly  back- 
wards, and  is  attached  to  the  ribs  of  the  sacral  vertebra. 

The  ischia  are  a  pair  of  somewhat  square  bones  which 
meet  one  another  in  the  middle  line ;  they  form  part  of  the 
acetabulum,  and  are  united  to  the  ilia  above. 

In  front  of  the  ischia  is  a  narrow  cartilaginous  area  which 
represents  the  pubes.  Projecting  forwards  from  it  is  a  bifid 
cartilaginous  epipubis. 

D.  THE  POSTERIOR  LIMB. 

This  is  divisible  into  a  proximal  portion,  the  thigh,  a 
middle  portion,  the  crus  or  shin,  and  a  distal  portion,  the 
pes. 

The  thigh  consists  of  a  single  bone,  the  femur  (fig.  23,  A,l), 
which  has  a  thin  shaft  and  expanded  ends.  The  anterior 
part  of  the  pre-axial  border  and  posterior  part  of  the  postaxial 
border  bear  slight  outgrowths. 

The'crus  or  shin  includes  two  short  bones,  the  tibia  and 
fibula,  which  are  nearly  equal  in  length.  The  pre-axial  bone 
or  tibia  is  a  straight  bone  thickest  at  its  proximal  end,  the 
postaxial  bone  or  fibula  (fig.  23,  A,  3)  is  a  rather  stouter 
curved  bone  of  nearly  equal  diameter  throughout. 

The  pes  includes  the  tarsus  or  ankle,  and  the  foot. 


150          THE  VERTEBRATE  SKELETON. 

The  tarsus  consists  of  eight  small  bones  arranged  in  a 
proximal  row  of  three,  the  tibiale,  intermedium  and  fibu- 
lare,  and  a  distal  row  of  four  tarsalia,  with  one  bone,  the 
centrale  (fig.  23,  A,  7),  interposed  between  the  two  rows. 
In  the  specimen  examined,  the  tibiale,  is  a  small  bone 
articulating  with  the  tibia,  the  intermedium  (fig.  23,  A,  5) 
is  larger  and  articulates  with  both  tibia  and  fibula,  the 
fibulare  is  the  largest  of  the  three  and  articulates  with  the 
fibula. 

The  bones  of  the  distal  row  are  tarsalia  1,  2,  3,  and  a 
bone  representing  4  and  5  fused.  In  the  specimen  examined 
tarsale  1  is  pushed  away  dorsal ly  (fig.  23,  A,  8),  so  as  to  lie 
between  the  tibiale  and  tarsale  2.  All  the  tarsal  bones  are 
small  and  somewhat  polygonal,  and  are  connected  with  one 
another,  and  with  the  tibia  and  fibula  on  the  one  hand,  and 
with  the  metatarsals  on  the  other  by  a  thin  layer  of  cartilage. 

The  five  digits  of  the  foot  each  consist  of  a  metatarsal 
and  of  a  certain  number  of  phalanges.  In  the  specimen 
examined,  owing  to  the  shifting  of  tarsale  1,  the  first  meta- 
tarsal as  well  as  the  second  articulates  with  tarsale  2,  while 
the  fifth  metatarsal  articulates  partially  with  the  bone  repre- 
senting the  fused  tarsalia  4  and  5,  partially  with  the  fibulare. 
All  the  bones  of  the  digits  except  the  distal  phalanges  are 
terminated  at  each  end  by  cartilaginous  epiphyses,  the  distal 
phalanx  of  each  digit  has  a  cartilaginous  epiphysis  only  on  its 
proximal  end. 

The  first,  second,  and  fifth  digits  have  two  phalanges 
apiece,  the  third  and  fourth  have  three. 

Figure  31  B,  showing  a  Newt's  tarsus  copied  from  Gegen- 
baur,  has  precisely  the  arrangement  generally  regarded  as 
primitive  for  the  higher  vertebrates,  except  that  tarsalia  4 
and  5  are  fused. 


CHAPTER   XL 


THE    SKELETON   OF  THE  FROG1  (Sana  temporaria). 

I.     EXOSKELETON. 

The  skin  of  the  frog  is  smooth  and  quite  devoid  of  scales 
or  other  exoskeletal  structures.  The  only  exoskeletal  struc- 
tures met  with  in  the  frog  are  : — 

1.  The  teeth,  which  are  most  conveniently  described  with 
the  endoskeleton. 

2.  The  horny  covering  of   the  calcar  or  prehallux  (see 
p.  167). 

II.     ENDOSKELETON. 

The  endoskeleton  of  the  adult  frog  consists  partly  of 
cartilage,  partly  of  bone  and  each  of  these  types  of  tissue 
occurs  in  two  forms.  The  cartilage  may  be  hyaline,  as  in 
the  omosternum  and  xiphisternum,  or  may  be  more  or  less 
calcined  as  in  part  of  the  suprascapula  and  the  epiphyses 
of  the  limb  bones.  The  bone  may  be  cartilage  bone,  or 
membrane  bone. 

The  skeleton  is  divisible  into  an  axial  portion  consisting 
of  the  skull,  vertebral  column,  and  sternum,  and  an  appen- 

1  See  A.  Ecker,  Die  anatomie  des  Frosches,  Braunschweig  1864, 
translated  by  G.  Haslam,  Oxford,  1889,  also  A.  M.  Marshall,  The  Frog, 
5th  edition,  Manchester  and  London,  1894. 


152          THE  VERTEBRATE  SKELETON. 

dicular  portion  consisting  of  the  skeleton  of  the  limbs  and 
their  girdles. 

1.     THE  AXIAL  SKELETON. 

A.     THE  VERTEBRAL  COLUMN. 

The  vertebral  column  is  a  tube,  formed  of  a  series  of  ten 
bones  which  surround  and  protect  the  spinal  cord.  Of  these 
ten  bones  nine  are  vertebrae,  while  the  tenth  is  a  straight  rod, 
the  urostyle,  and  is  almost  as  long  as  all  the  vertebrae  put 
together.  The  second  to  eighth  vertebrae  inclusive  have  a  very 
similar  structure,  but  the  first  and  ninth  differ  from  the  others. 

Any  one  of  the  second  to  eighth  vertebrae  forms  a  bony 
ring  with  a  somewhat  thickened  floor,  the  centrum  or  body, 
which  articulates  with  the  centra  of  the  immediately  preceding 
and  succeeding  vertebrae.  The  articulating  surfaces  are 
covered  with  cartilage  and  are  procoelous,  or  convex  in  front 
and  concave  behind.  The  eighth  vertebra  is  however  amphi- 
coelous  or  biconcave.  The  centrum  of  each  vertebra  encloses 
an  isolated  vestige  of  the  notochord.  The  neural  arch  forms 
the  roof  and  sides  of  the  neural  canal,  which  is  very  spacious 
in  the  anterior  vertebrae,  but  becomes  more  depressed  in  the 
posterior  ones.  The  arch  bears  the  neural  spine,  a  low 
median  ridge  of  variable  character,  and  is  drawn  out  in 
front  and  behind,  forming  the  two  pairs  of  articulating 
surfaces  or  zygapophyses  by  means  of  which  the  vertebrae 
are  attached  together.  Of  these  the  anterior  articulating 
surfaces  or  prezygapophyses  look  upwards  and  slightly 
inwards,  while  the  posterior  articulating  surfaces  or  post- 
zygapophyses  look  downwards  and  slightly  outwards.  The 
sides  of  the  neural  arches  are  drawn  out  into  a  pair  of 
prominent  transverse  processes.  Those  of  the  second 
vertebra  look  somewhat  forwards,  those  of  the  third  look 
directly  outwards  or  somewhat  forwards,  while  those  of 
the  fourth,  fifth,  and  sixth  are  directed  slightly  backwards, 
and  those  of  the  seventh  and  eighth  nearly  straight  outwards. 


THE  SKELETON  OF  THE  FROG.      SPECIAL  VERTEBRAE.     153 

All  the  transverse  processes  are  terminated  by  very  small  carti- 
laginous ribs. 

SPECIAL  VERTEBRAE. 

The  first  vertebra  is  a  ring-like  structure  with  a  much 
depressed  centrum.  It  bears  in  front  two  oval  concave  sur- 
faces for  articulation  with  the  condyles  of  the  skull,  while  the 
centrum  is  terminated  behind  by  a  prominent  convex  surface. 
There  are  as  a  rule  no  transverse  processes,  and  the  post- 
zygapophyses  look  downwards  and  outwards.  Occasionally 
however  transverse  processes  do  occur.  Projecting  forwards 
from  the  centrum  is  a  minute  process  better  developed  in  the 
Newt.  This  resembles  an  odontoid  process,  and  it  has  hence 
been  supposed  that  the  first  vertebra  is  homologous  with  the 
axis  of  mammalia,  and  that  the  atlas  of  the  frog  is  fused  with 
the  skull. 

The  ninth  vertebra  has  very  stout  transverse  processes 
directed  backwards  and  somewhat  upwards.  They  articulate 
with  the  pelvic  girdle  and  hence  this  vertebra  is  regarded  as 
the  sacrum.  The  neural  arch  is  much  depressed,  the  centrum 
is  convex  in  front  and  bears  on  its  posterior  surface  two  short 
rounded  processes  for  articulation  with  the  urostyle. 

The  urostyle  is  a  long  rod-like  bone  forming  the  posterior 
unsegmented  continuation  of  the  vertebral  column.  It  is 
probably  equivalent  to  three  vertebrae,  the  tenth,  eleventh, 
and  twelfth  fused  together,  and  to  an  unsegmented  rod  of 
cartilage  which  lies  ventral  to  the  notochord.  The  anterior  end 
is  expanded  and  bears  two  concave  articular  surfaces  by  means 
of  which  it  articulates  with  the  sacrum.  A  prominent  ridge 
runs  along  the  dorsal  surface,  but  gradually  diminishes  when 
traced  back.  The  anterior  portion  contains  a  canal  which  is 
a  continuation  of  the  neural  canal.  At  a  point  not  far  from 
the  anterior  end,  this  canal  communicates  with  the  exterior 
by  a  pair  of  minute  holes  which  correspond  with  the  iiiter- 
vertebral  foramina. 


154          THE  VERTEBRATE  SKELETON. 

B.  THE  SKULL1. 

The  skull  of  the  Frog  consists  of  three  principal  parts  : — 

(1)  an  axial  part,  the  cranium,  proper,  which  encloses 
the  brain.     To  it  are  firmly  fused 

(2)  the    capsules    of   the    olfactory    and    auditory 
sense  organs, 

(3)  lastly  there  is  the  hyoid  apparatus  and  the  skele- 
ton of  the  jaws. 

The  skull  is  by  no  means  so  completely  ossified  as  is  the 
vertebral  column,  but  in  addition  to  the  cartilage  bone,  there 
is  a  great  development  of  membrane  bone  in  connection 
with  it. 

The  skull  has  a  peculiarly  flattened  and  expanded  form 
depending  on  the  wide  lateral  separation  of  the  jaws  from  the 
cranium. 

(1)     THE  CRANIUM  PROPER  or  Brain  case. 

This  is  an  unsegmented  tube,  which  is  widest  behind.  It 
remains  to  a  considerable  extent  cartilaginous,  but  is  partly 
converted  into  cartilage  bone,  partly  sheathed  in  membrane 
bone.  Its  roof  is  imperfect,  being  pierced  by  three  holes 
or  fontanelles,  one  large  anterior  fontanelle  (fig.  25,  A,  9), 
and  two  smaller  posterior  fontanelles  (fig.  25,  A,  10). 

The  cartilage  bones  of  the  cranium  proper  are  the  two 
exoccipitals  and  the  sphenethmoid. 

The  exoccipitals  (figs.  24,  25,  and  26,  6)  are  a  pair  of 
irregular  bones  bounding  the  foramen  magnum  at  the  posterior 
end  of  the  skull.  They  almost  completely  surround  the  foramen 
magnum,  and  bear  a  pair  of  oval  convex  surfaces,  the  occipital 
condyles,  with  which  the  first  vertebra  articulates.  The  bones 
generally  called  the  exoccipitals  of  the  frog  include  the  epi-otic 

1  W.  K.  Parker,  Phil.  Trans.  161,  1871,  p.  137,  and  W.  K.  Parker  and 
G.  T.  Bettany,  The  Morphology  of  the  Skull,  London,  1877,  p.  136. 


THE  SKELETON  OF  THE  FROG.   THE  SKULL.    155 


and  opisthotic  elements  of  many  skulls,  in  addition  to  the 
exoccipitals. 

The  patch  of  unossified  cartilage  immediately  external. to 
the  occipital  condyle  is  pierced  by  two  small  foramina,  through 
which  the  ninth  and  tenth  nerves  leave  the  cranial  cavity. 
The  ninth  nerve  passes  through  the  more  external  of  these 
foramina,  the  tenth  through  the  one  nearer  the  condyle. 

A  B 


20 


FlG.    24.      A   DORSAL,    AND    B   VENTRAL   VIEWS    OF    THE    CRANIUM    OF    A 

COMMON  FROG  (Rana  temporaria)  x  2  (after  PARKER). 

In  this  and  the  next  two  figs,  cartilage  is  dotted,  cartilage  bones  are 
marked  with  dots  and  dashes,  membrane  bones  are  left  white. 


1.  sphenethmoid. 

2.  fronto-parietal. 

3.  pterygoid. 

4.  squamosal. 

6.  exoccipital. 

7.  parasphenoid. 

8.  pro-otic. 

9.  quadratojugal. 

10.  maxilla. 

11.  nasal. 

12.  premaxilla. 

13.  anterior  nares. 


14.  vomer. 

15.  posterior  nares. 

16.  palatine. 

18.  columella. 

19.  quadrate. 

20.  occipital  condyle. 
II.     optic  foramen. 

V.  VII.  foramen  for  exit  of 
trigeminal  and  facial  nerves. 

IX.  X.  foramina  for  exit  of  glos- 
sopharyngeal  and  pneumogastric 


156          THE  VERTEBRATE  SKELETON. 

The  foramina  lie  however  very  close  together  and  are  some- 
times confluent.  The  cranial  walls  for  a  considerable  distance 
in  front  of  the  occipitals  are  unossified,  but  the  anterior  end 
of  the  cranial  cavity  is  encircled  by  another  cartilage  bone,  the 
sphenethmoid  (figs.  24  and  25,  1)  or  girdle  bone.  This 
partly  corresponds  to  the  orbitosphenoids  of  the  Newt's  skull. 
Anteriorly  it  is  pierced  by  a  pair  of  small  foramina  through 
which  the  ophthalmic  branches  of  the  trigeminal  nerve  pass  out. 

The  anterior  part  of  the  cranial  cavity  is  divided  into  two 
halves  by  a  vertical  plate,  the  mesethmoid.  Some  little 
distance  behind  the  sphenethmoid  the  ventro-lateral  walls  of 
the  cartilaginous  cranium  are  pierced  by  a  pair  of  rather  pro- 
minent holes,  the  optic  foramina  (figs.  24  and  25,  B,  n),  and 
at  a  similar  distance  further  back,  occupying  a  kind  of  notch 
in  the  pro-otic  are  the  large  trigeminal  foramina,  through 
which  the  fifth  and  seventh  nerves  leave  the  cranium.  Between 
the  trigeminal  and  optic  foramina  are  the  very  small  foramina 
for  the  sixth  nerves  (fig.  25,  B,  vi). 

The  membrane  bones  of  the  cranium  proper  include  the 
fronto-parietals  and  the  parasphenoid. 

The  fronto-parietals  (figs.  24  and  26,  A,  2)  form  a  pair  of 
long  flat  bones  closely  applied  to  one  another  in  the  middle  line, 
the  line  of  junction  being  the  sagittal  suture.  They  cover 
over  the  fontanelles  and  overlap  the  sphenethmoid  in  front. 

The  parasphenoid  (figs.  24  and  26,  B,  7)  is  a  bone  shaped 
like  a  dagger  with  a  very  short  handle.  It  lies  on  the  ventral 
surface  of  the  cranium,  the  blade  being  directed  forwards  and 
underlying  the  sphenethmoid;  its  lateral  processes  underlie 
the  auditory  capsules.  i 

(2)     THE  SENSE  CAPSULES. 

The  sense  capsules  are  cartilaginous  or  bony  structures 
which  surround  the  olfactory  and  auditory  organs  and  are 
closely  united  to  the  cranium. 

The  auditory  capsules  are  fused  with  the  sides  of  the 


THE   SKELETON    OF   THE    FROG.      THE   SKULL.        157 


posterior  end  of  the  cranium  just  in  front  of  the  exoccipitals. 
They  are  largely  cartilaginous,  but  include  in  their  anterior 

A  B 


FlG.    25.       A   DOKSAL   AND    B    VENTRAL    VIEW    OF  THE   CRANIUM  OF  A  COMMON 

FROG  (Eana  temporaria)   from   which   the   membrane   bones   have 
mostly  been  removed.  x2  (after  PARKER). 


1.  sphenethmoid. 

2.  palatine. 

3.  pterygoid. 

4.  quadrate. 

5.  columella. 
6»  exoccipital. 

7.  ventral  cartilaginous  wall  of 
cranium. 


8. 


pro-otic. 
9.     anterior  fontanelle. 

10.  right  posterior  fontanelle. 

11.  quadratojugal. 

12.  nasal  capsule. 

II.  V.  VI.  IX.  X.  foramina  for 
exit  of  cranial  nerves. 


walls  a  pair  of  irregular  cartilage  bones,  the  pro-otics  (figs. 
24  and  25,  8).  The  cartilaginous  area  lying  ventral  to  the 
pro-otic  and  external  to  the  exoccipital  is  pierced  by  a  rather 
prominent  hole,  the  fenestra  ovalis,  which  forms  a  com- 
munication between  the  internal  ear  cavity,  and  a  space  the 
tympanic  cavity,  which  lies  at  the  side  of  the  head,  and  is 
bounded  externally  by  the  tympanic  membrane.  The  fenestra 
ovalis  is  occupied  by  a  minute  cartilaginous  structure,  the 
stapes,  and  articulated  partly  to  this  and  partly  to  a  slight 
recess  in  the  pro-otic  is  the  columella  (fig.  25,  B,  5),  a  rod  in 
part  bony  and  in  part  cartilaginous,  whose  outer  end  is 


158  THE  VERTEBRATE  SKELETON. 

attached  to  the  tympanic  membrane.  The  columella  and 
stapes  are  together  homologous  with  the  mammalian  auditory 
ossicles  and  with  the  hyomandibular  of  Elasmobranchs.  Some- 
times the  term  columella  is  used  to  include  the  whole  ossicular 
chain, — the  columella  together  with  the  stapes. 

The  olfactory  or  nasal  capsules  (fig.  25,  B,  12)  are  fused 
with  the  anterior  end  of  the  cranium  and  differ  from  the 
auditory  capsules  in  being  to  a  great  extent  unossified.  There 
are  however  two  pairs  of  membrane  bones  developed  in  con- 
nection with  them,  the  vomers  and  the  nasals.  They  are  drawn 
out  into  three  pairs  of  cartilaginous  processes,  on  the  dorsal 
surface  into  the  prenasal  and  alinasal  processes  which  bound 
the  external  nares,  and  on  the  ventral  surface  towards  the 
middle  line  into  the  forwardly-projecting  rhinal  processes. 

The  nasals  (figs.  24  and  26,  11)  form  a  pair  of  triangular 
bones  lying  dorso-laterally  in  front  of  the  fronto-parietals. 
Their  bases  are  turned  towards  one  another  and  their  apices 
are  directed  outwards  and  backwards.  They  correspond  in 
position  with  the  prefrontals  of  the  reptilian  skull  as  well  as 
with  the  nasals. 

The  vomers  are  a  pair  of  irregular  bones  lying  on  the 
ventral  surface  of  the  olfactory  capsules.  Each  bears  on 
its  inner  and  posterior  angle  a  group  of  minute  pointed  teeth, 
while  its  outer  border  is  drawn  out  into  three  or  four  small 
slightly  diverging  processes,  the  two  posterior  of  which  form 
the  inner  boundary  of  the  posterior  nares  (fig.  24,  B,  15). 

(3)     THE  JAWS. 

The  upper  jaw  consists  of  a  rod  of  cartilage  connected 
with  the  cranium  near  its  two  ends,  but  widely  separated  from 
it  in  the  middle.  It  is  almost  completely  overlain  by  membrane 
bone.  With  its  posterior  end  the  lower  jaw  articulates. 

The  membrane  bones  of  the  upper  jaw  include  first  the 
premaxilla,  a  small  bone  meeting  its  fellow  in  the  middle 
line,  and  forming  the  extreme  anterior  end  of  the  upper  jaw. 
It  gives  off  on  its  dorsal  surface  a  backwardly-projecting 


THE  SKELETON  OF  THE  FROG.   THE  SKULL.    159 


process.     It  is  connected  behind  with  the  maxilla  (figs.  24  and 
26,  10),  a  long  flattened  bone  which  forms  the  greater  part  of 


FIG.  26.     A,  LATERAL  VIEW  OF 

CRANIUM    OF   A    COMMON    FROG 

1.  sphenethmoid. 

2.  fronto-parietal. 

3.  pterygoid. 

4.  squamosal. 

5.  tympanic  membrane. 

6.  exoccipital. 

7.  parasphenoid. 

8.  pro-otic. 

9.  quadratojugal, 

10.  maxilla. 

11.  nasal. 

12.  premaxilla. 

13.  anterior  nares. 


B 


THE    SKULL,     B,    POSTERIOR    VIEW    OF    THE 

(Rana  temporaria)  x  2  (after  PARKER). 

14.  mento-meckelian. 

15.  dentary. 

16.  angulo-splenial. 

17.  basilingual  plate. 

19.  quadrate. 

20.  columella. 

21.  occipital  condyle. 

22.  anterior  cornu  of  the  hyoid 

(cerato-hyal). 

23.  foramen  magnum. 

II.  IX.  X.  foramina  for  the  exit 
of  cranial  nerves. 


the  margin  of  the  upper  jaw,  and  gives  off  near  its  anterior  end 
a  short  process  which  projects  upwards  and  meets  the  nasal. 

Both  maxilla  and  premaxilla  are  grooved  ventrally,  and 
bear,  attached  to  the  outer  more* prominent  margin  of  the  groove, 
a  row  of  minute  conical  teeth.  These  teeth  are  pleurodont, 
that  is,  are  ankylosed  by  their  bases  and  outer  sides  to  the 
margin  of  the  jaw.  Each  tooth  is  a  hollow  cone,  the  basal 


160          THE  VERTEBRATE  SKELETON. 

part  of  which  is  formed  of  bone,  the  apical  part  of  dentine, 
capped  by  a  very  weak  development  of  enamel. 

The  posterior  end  of  the  maxilla  is  overlapped  by  a  small 
bone,  the  quadratojugal  (figs.  24  and  26,  9),  whose  posterior 
end  forms  part  of  the  articular  surface  for  the  lower  jaw. 
Just  behind  the  quadratojugal  there  is  a  small  unossified  area 
which  lies  at  the  angle  of  the  mouth,  and  is  connected  by  a 
narrow  bar  of  cartilage  with  the  cranium ;  this  forms  the 
quadrate  (figs.  24  and  26,  19).  A  backwardly-directed  out- 
growth from  the  cartilaginous  bar  more  or  less  completely 
surrounds  the  tympanic  membrane,  forming  the  tympanic 
ring.  When  followed  back  the  maxilla  and  quadratojugal 
diverge  further  and  further  from  the  cranium,  till  the  angle 
of  the  mouth  comes  to  be  separated  from  the  foramen  magnum 
by  a  space  nearly  double  the  width  of  the  cranium.  This  space 
is  bridged  over  to  a  considerable  extent  by  two  triradiate  bones, 
the  pterygoid  and  squamosal. 

The  pterygoid  (figs.  24  and  26,  3)  is  a  large  bone,  whose 
anterior  limb  runs  forwards  meeting  the  maxilla  and  palatine; 
while  its  inner  limb  meets  the  auditory  capsule  and  para- 
sphenoid,  and  its  outer  limb  runs  backwards  and  outwards 
to  the  angle  of  the  mouth.  The  palatine  is  a  small  transversely- 
placed  bone,  which  connects  the  pterygoid  with  the  anterior 
part  of  the  sphenethmoid.  The  squamosal  (figs.  24  and  26,  4) 
is  a  T-shaped  bone  whose  anterior  arm  is  pointed  and  passes 
forwards  to  meet  the  pterygoid.  The  posterior  upper  arm  is 
closely  applied  to  the  pro-otic,  while  the  posterior  lower  arm 
meets  the  pterygoid  and  quadratojugal  at  the  angle  of  the  jaw, 
and  surrounds  the  narrow  cartilaginous  bar  of  the  quadrate 
which  goes  to  join  the  cranium.  The  squamosal  is  probably 
homologous  with  the  squamosal  together  with  the  pre-opercular 
of  Bony  Ganoids. 

The  quadrate  and  squamosal  form  the  suspensorium.  by 
which  the  lower  jaw  is  connected  with  the  cranium. 

The  lower  jaw  or  mandible  consists  of  a  pair  of  carti- 
laginous rods  (Meckel's  cartilages)  in  connection  with  each 


THE  SKELETON  OF  THE  FROG.   THE  HYOID.    161 

of  which  there  are  developed  two  membrane  bones  and  one 
cartilage,  bone.  The  cartilage  bone  is  the  mento-meckelian 
(fig.  26,  A,  14),  a  very  small  ossification  at  the  extreme  anterior 
end.  The  membrane  bones  are  the  angulo-splenial  and  the 
dentary.  The  angulo-splenial  is  a  strong  flat  bone  which  forms 
the  inner  and  lower  part  of  the  mandible  for  the  greater 
part  of  its  length.  Its  dorsal  surface  is  produced  into  a  slight 
coronoid  process.  The  dentary  (fig.  26,  A,  15)  is  a  flat 
plate  which  covers  the  outer  surface  of  the  anterior  half  of  the 
mandible,  as  far  forwards  as  the  mento-meckelian.  The  lower 
jaw  is  devoid  of  teeth.  The  part  of  Meckel's  cartilage  which 
in  most  vertebrates  ossifies,  forming  the  articular  bone,  remains 
unossified  in  the  Frog. 

THE  HYOID  APPARATUS. 

The  hyoid  of  the  adult  Frog  is  formed  of  the  modified 
hyoid  and  branchial  arches  of  the  tadpole.  It  consists  of  a 
broad  thin  plate  of  cartilage,  the  basilingual  plate  (fig.  29, 
B,  1),  drawn  out  into  two  pairs  of  long  processes,  the  comua. 
The  basilingual  plate  is  broader  in  front  than  behind,  and  is 
formed  from  the  fused  ventral  ends  of  the  hyoid  and  branchial 
arches  of  the  tadpole. 

The  anterior  cornua  (fig.  29,  B,  2)  form  a  pair  of  long 
slender  cartilaginous  rods  which  project  from  the  body  of  the 
hyoid  at  first  forwards,  then  backwards,  and  finally  upwards 
and  somewhat  forwards  again,  to  be  united  to  the  auditory 
capsules  just  below  the  fenestrae  ovales.  They  are  formed 
from  the  dorsal  portion  of  the  hyoid  arch  of  the  tadpole  and 
are  homologous  with  the  cerato-hyals  of  the  Dogfish. 

The  posterior  cornua  form  a  pair  of  straight  bony  rods 
diverging  outwards  from  the  posterior  end  of  the  basilingual 
plate.  They  are  formed  from  the  fourth  branchial  arches  of 
the  tadpole,  and  differ  from  the  rest  of  the  hyoid  apparatus 
in  being  well  ossified. 

R.  11 


162          THE  VERTEBRATE  SKELETON. 

The  columellar  chain,  which  has  been  already  described 
(p.  157),  should  be  mentioned  with  the  hyoid  as  it. is  homo- 
logous to  the  hyomandibular  of  fishes. 

The  sternum,  of  the  Frog,  though  regarded  as  part  of  the 
axial  skeleton,  is  so  intimately  connected  with  the  pectoral 
girdle,  that  it  will  be  described  with  the  appendicular 
skeleton. 

2.     THE  APPENDICULAR  SKELETON. 

This  consists  of  the  skeleton  of  the  two  pairs  of  limbs  and 
their  respective  girdles.  It  is  at  first  entirely  cartilaginous 
but  the  cartilage  becomes  later  on  mainly  replaced  by  bone. 
The  only  bone  developed  in  connection  with  the  appendi- 
cular skeleton,  which  has  no  cartilaginous  predecessor,  is  the 
clavicle. 

A.     THE  PECTORAL  GIRDLE. 

This  consists  originally  of  two  half  rings  of  cartilage  en- 
circling the  sides  of  the  body  a  short  way  behind  the  head. 
These  two  halves  meet  one  another  in  the  ventral  middle  line, 
and  separate  the  anterior  elements  of  the  sternum  from  the 
posterior  ones. 

Each  half -ring  bears  on  the  middle  of  its  outer  and  pos- 
terior surface  a  prominent  cup,  the  glenoid  cavity,  with 
which  the  proximal  arm-bone  articulates.  This  cup  divides 
the  half-arch  into  a  dorsal  scapular  and  a  ventral  coracoid 
portion. 

The  scapular  portion  consists  of  two  parts,  the  supra- 
scapula  and  the  scapula. 

The  suprascapula  (fig.  30,  A,  2)  is  a  wide,  thin  plate 
attached  by  its  ventral  and  narrowest  border  to  the  scapula. 
Its  proximal  and  anterior  half  is  imperfectly  ossified,  its  whole 
border  or  sometimes  only  its  dorsal  and  posterior  borders  consist 
of  unaltered  hyaline  cartilage,  while  the  rest  of  it  is  composed 
of  calcified  cartilage.  The  scapula  (fig.  30,  A,  3)  is  a  fairly 


THE   SKELETON    OF   THE    FROG.      THE    STERNUM.     163 

stout  rod  of  bone  constricted  in  the  middle,  and  forming  the 
dorsal  half  of  the  glenoid  cavity. 

The  coracoid  portion  consists  of  three  parts,  the  cora- 
coid,  precoracoid  and  clavicle. 

The  largest  and  most  posterior  of  these  is  the  coracoid 
(fig.  30,  A,  4)  which  like  the  scapula,  is  contracted  in  the 
middle  and  expanded  at  the  ends,  especially  at  the  ventral 
end.  It  forms  a  large  part  of  the  glenoid  cavity.  The 
ventral  ends  of  the  coracoids  which  meet  one  another  in  the 
middle  line  are  unossified,  and  form  narrow  strips  of  calcified 
cartilage,  the  epicoracoids  (fig.  30,  A,  5) ;  these  are  often 
regarded  as  sternal  elements. 

The  precoracoid  forms  a  narrow  strip  of  cartilage  lying 
in  front  of  the  coracoid,  from  which  it  is  separated  by  the 
wide  coracoid  foramen  (fig.  30,  A,  9).  The  dorsal  end  is 
continuous  with  an  area  of  unossified  cartilage  which  separates 
the  coracoid  and  scapula  and  forms  part  of  the  glenoid  cavity. 

The  clavicle  is  a  narrow  membrane  bone  closely  attached 
to  the  anterior  surface  of  the  precoracoid,  its  dorsal  end  is  ex- 
panded. 

THE  STERNUM. 

The  sternum  consists  of  four  parts  arranged  in  two  groups ; 
two  parts  to  each  group.  The  anterior  members  are  the  epi- 
sternum  and  omosternum. 

The  episternum  (fig.  30,  A,  10)  is  a  thin  almost  circular 
plate  of  cartilage  much  of  which  remains  hyaline. 

The  omosternum  (fig.  30,  A,  11)  is  a  slender  bony  rod 
widest  at  its  posterior  end  :  it  connects  the  episternum  with 
the  ventral  ends  of  the  precoracoids. 

The  sternum  proper  is  a  short  rod  of  cartilage  sheathed 
in  bone ;  it  is  contracted  in  the  middle  and  expanded  at  each 
end.  It  bears  attached  to  its  posterior  end  a  broad  some- 
what bilobed  plate  of  partially  calcified  cartilage,  the  xiphi- 
sternum  (fig.  30,  A,  13). 

11—2 


164          THE  VERTEBRATE  SKELETON. 

B.     THE  ANTERIOR  LIMB. 

This  is  divisible  into  three  parts,  the  upper  arm  or 
brachium,  the  fore-arm  or  antibrachium,  and  the  maims. 

All  the  larger  bones  have  their  ends  formed  by  prominent 
epiphyses  which  do  not  unite  with  the  shaft  till  late  in  life. 
Their  articulating  surfaces  are  covered  by  hyaline  cartilage. 

In  the  upper  arm  there  is  a  single  bone,  the  humerus. 

This  has  a  more  or  less  cylindrical  shaft  and  articulates  by 
a  prominent  rounded  head  with  the  glenoid  cavity.  The 
distal  end  shows  a  large  rounded  swelling  on  either  side  of 
which  is  a  condylar  ridge,  the  inner  or  postaxial  one  being 
the  larger.  A  prominent  deltoid  ridge  runs  along  the 
proximal  half  of  the  anterior  surface,  and  in  the  male  frog  a 
second  equally  prominent  ridge  runs  along  the  distal  half  of 
the  posterior  surface. 

The  fore-arm  consists  of  two  bones,  the  radius  and  ulna, 
united  together  and  forming  the  radio-ulna.  The  two  bones 
are  quite  fused  at  their  proximal  ends  where  they  form  a 
deep  cup  which  articulates  with  the  distal  end  of  the  humerus, 
and  is  drawn  out  into  a  rather  prominent  backwardly-pro- 
jecting  olecranon  process,  which  ossifies  from  a  centre 
distinct  from  that  of  the  shaft.  The  distal  end  is  distinctly 
divided  by  a  groove  into  an  anterior  radial  and  a  posterior 
ulnar  portion. 

The  manus  consists  of  two  parts,  the  wrist  or  carpus 
and  the  hand. 

The  carpus1  consists  of  six  small  bones  arranged  in  two 
rows.  The  three  bones  of  the  proximal  row  are  the  ulnare, 
radiale  and  centrale.  The  ulnare  and  radiale  are  about 
equal  in  size  and  articulate  regularly  with  the  radio-ulna.  The 
centrale  is  pushed  out  of  its  normal  position  and  lies  partly  on 
the  pre-axial  side,  partly  in  front  of  the  radiale.  Of  the  three 
bones  of  the  distal  row  the  two  pre-axial  ones,  carpalia  1  and 
2,  are  small;  carpale  2  articulates  with  the  second  metacarpal, 
1  See  G.  B.  Howes  and  W.  Ridewood,  P.  Z.  S.,  1888,  p.  141.  * 


THE   SKELETON    OF   THE    FROG.      PELVIC   GIRDLE.    165 

carpale  1  with  both  the  first  and  second.  The  third  bone  is 
large  and  articulates  with  the  third,  fourth  and  fifth  meta- 
carpals,  it  represents  carpalia  3 — 5,  with  probably  in  addition 
the  representative  of  a  second  centrale. 

The  hand  consists  of  four  complete  digits,  and  a  vestigial 
pollex  reduced  to  a  short  metacarpal. 

Each  of  the  four  complete  digits  consists  of  a  metacarpal 
and  a  variable  number  of  phalanges.  The  first  digit,  as  just 
mentioned,  has  no  phalanges,  the  second  and  third  have  two, 
and  the  fourth  and  fifth  have  three. 

C.     THE  PELVIC  GIRDLE. 

The  pelvic  girdle  of  the  Frog  is  much  modified  from  the 
simple  or  general  type  found  in  the  Newt  (p.  149). 

It  is  a  V-shaped  structure  consisting  of  two  halves  which 
are  fused  together  in  the  middle  line  posteriorly,  while  in 
front  they  are  attached  to  the  ends  of  the  transverse  pro- 
cesses of  the  sacral  vertebra.  Each  half  bears  at  its  posterior 
end  a  deep  cup,  the  acetabulum,  with  which  the  head  of  the 
femur  articulates. 

Each  half  of  the  pelvis  ossifies  from  two  centres.  The 
anterior  and  upper  half  of  the  acetabulum,  and  the  long 
laterally  compressed  bar  extending  forwards  to  meet  the  sacral 
vertebra  ossify  from  a  single  centre  and  are  generally  called 
the  ilium ;  it  is  probable  however  that  they  represent  both 
the  ilium  and  pubis  of  mammals1.  The  posterior  part  of 
this  bone  meets  its  fellow  in  a  median  symphysis. 

The  posterior  third  of  the  acetabulum  is  formed  by  a  small 
bone,  the  ischium,  which  likewise  meets  its  fellow  in  a 
median  symphysis. 

The  ventral  portion  of  the  pelvic  girdle  never  ossifies,  even 
in  old  animals  being  formed  only  of  calcified  cartilage.  This 
is  generally  regarded  as  the  pubis,  but  it  perhaps  corresponds 
to  the  acetabular  bone  of  mammals. 

1  See  bottom  of  p.  187. 


166  THE  VERTEBRATE  SKELETON. 

D.     THE  POSTERIOR  LIMB. 

This  corresponds  closely  to  the  anterior  limb  and,  like  it, 
is  divisible  into  three  parts,  the  thigh,  the  shin  or  cms  and 
the  pes. 

As  was  the  case  with  the  anterior  limb,  all  the  long  bones 
have  their  ends  formed  by  prominent  epiphyses  which  do  not 
unite  with  the  shaft  till  late  in  life. 

In  the  thigh  there  is  only  a  single  bone,  the  femur. 

The  femur  is  a  moderately  long,  slender  bone  with  a  well- 
ossified  hollow  shaft  slightly  curved  in  a  sigmoid  manner. 
Both  ends  are  expanded,  the  proximal  end  is  hemispherical 
and  articulates  with  the  acetabulum,  the  distal  end  is  larger 
and  more  laterally  expanded. 

The  shin  likewise  includes  a  single  bone,  the  tibio-fibula, 
but  this,  as  can  be  readily  seen  by  the  grooves  at  the  proximal 
and  distal  ends  of  the  shaft,  is  formed  by  the  fusion  of  two 
distinct  bones,  the  tibia  and  fibula.  The  tibio-fibula  is  longer 
and  straighter  than  the  femur. 

The  pes  consists  of  two  parts,  the  ankle  or  tarsus  and  the 
foot. 

The  tarsus  consists  of  two  rows  of  structures,  very  dif- 
ferent in  size.  The  proximal  row  consists  of  two  long  bones, 
the  tibiale  and  fibulare,  which  are  united  by  common  epi- 
physes at  the  two  ends,  while  in  the  middle  they  are  widely 
separated.  The  tibiale  lies  on  the  tibial  or  pre-axial  side, 
and  the  fibulare  which  is  the  larger  of  the  two  bones  on 
the  fibular  or  postaxial  side.  The  distal  row  of  tarsals 
consists  of  three  very  small  pieces  of  calcified  cartilage.  The 
postaxial  of  these  is  the  largest,  it  articulates  with  the  second 
and  third  metatarsals  and  is  probably  homologous  with  tarsalia 
2  and  3  fused.  The  middle  one  is  very  small,  it  articulates 
with  the  first  nietatarsal  and  is  probably  tarsale  1.  The  pre- 
axial  one  articulates  with  the  nietatarsal  of  the  calcar,  a 
structure  to  be  described  immediately,  and  has  been  regarded 
as  a  centrale. 


THE  SKELETON  OF  THE  FKOG.   THE  FOOT.    167 

The  foot  includes  five  complete  digits  and  a  supplemental 
toe  as  well.  Each  of  the  five  digits  consists  of  a  long  meta- 
tarsal  with  epiphyses  at  both  ends,  and  of  a  variable  number 
of  phalanges.  The  first  digit  or  hallux  and  the  second  have 
two  phalanges,  the  third  three,  the  fourth,  which  is  the  largest, 
four,  and  the  fifth,  three.  The  distal  phalanges  have  epi- 
physes only  at  their  proximal  ends,  the  others  at  both  ends. 

On  the  pre-axial  side  of  the  hallux  is  the  supplemental 
digit,  the  prehallux  or  calcar.  It  consists  of  a  short  meta- 
tarsal  and  one  or  two  phalanges,  and  is  terminated  distally  by 
a  horny  covering  of  epidermal  origin. 


CHAPTER    XII. 

GENERAL    ACCOUNT    OF    THE    SKELETON    IN 
AMPHIBIA. 

EXOSKELETON. 

The  exoskeleton,  at  any  rate  in  most  living  forms,  is  very 
slightly  developed  in  Amphibia.  The  only  representatives 
of  the  epidermal  exoskeleton  are  (1)  the  minute  horny  beaks 
found  coating  the  premaxillae  and  dentaries  in  Siren  and  the 
tadpoles  of  most  Anura,  (2)  the  nails  borne  by  the  first  three 
digits  of  the  pes  in  Xenopus  and  by  the  Japanese  Salamander 
Onychodactylus,  (3)  the  horny  covering  of  the  calcar  or  pre- 
hallux  of  frogs.  The  Urodela  and  nearly  all  the  Anura,  which 
form  the  vast  majority  of  living  Amphibia,  have  naked  skins. 
A  few  Anura  belonging  to  the  genera  Ceratophrys  and  Brachy- 
cephalus  have  bony  dermal  plates  developed  in  the  skin  of  the 
back,  and  these  plates  become  united  with  some  of  the  under- 
lying vertebrae. 

In  the  Gymnophiona  the  integument  bears  small  cycloid 
scales  arranged  in  rings  which  are  equal  in  number  to  the 
vertebrae.  These  scales  contain  calcareous  concretions.  Scales 
also  occur  between  the  successive  rings. 

In  the  Labyrinthodontia  the  dermal  exoskeleton  is  in 
many  genera  greatly  developed.  It  is  generally  limited  to  the 
ventral  surface  and  consists  principally  of  a  buckler  formed 
of  three  bony  plates,  one  median  and  two  lateral.  These 


THE    SKELETON    IN   AMPHIBIA.      THE   TEETH.          169 

plates  protect  the  anterior  part  of  the  thorax,  and  are  closely 
connected  with  the  adjacent  endoskeleton.  They  probably 
represent  the  interclavicle  and  clavicles.  Behind  this  buckler 
numerous  scutes  are  generally  developed,  which  often  cover 
the  whole  ventral  surface,  and  may  cover  the  whole  body. 

TEETH1. 

In  Amphibia  teeth  are  generally  present  on  the  maxillae, 
premaxillae  and  vomers,  and  except  in  Anura  on  the  dentaries  ; 
sometimes  they  occur  on  the  palatines  as  in  many  Urodela,  most 
Labyrinthodontia,  and  the  Gymnophiona;  less  commonly  on  the 
pterygoids  as  in  Menobranchus,  Siredon,  some  Labyrinthodontia, 
and  Pelobates  cultripes*,  or  on  the  splenials  as  in  Siren  and  Meno- 
branchus,  or  parasphenoid  as  in  Pelobates  cultripes,  Spelerpes 
belli  and  Batrachoseps.  In  some  Anura  such  as  Bufo  and  Pipa 
the  jaws  are  toothless. 

In  Gymnophiona,  Menobranchus,  and  Siredon,  the  teeth 
are  arranged  in  two  concentric  curved  rows.  The  teeth  of  the 
outer  row  are  borne  on  the  premaxillae  and  maxillae  if  present, 
(the  maxillae  are  absent  in  Menobranchus),  the  teeth  of  the 
second  row  on  the  vomers  and  pterygoids  in  Menobranchus 
and  Siredon,  and  on  the  vomers  and  palatines  in  Gymnophiona. 
In  some  Gymnophiona  there  is  a  double  row  of  mandibular 
teeth.  The  vomerine,  palatine  and  parasphenoid  teeth  of  all 
forms  are  numerous  and  are  not  arranged  in  rows. 

The  teeth  of  all  living  Amphibia  are  simple  conical  struc- 
tures ankylosed  to  the  bone,  and  consisting  of  dentine,  coated 
or  capped  with  a  thin  layer  of  enamel.  In  the  Labyrinthodontia 
teeth  of  more  than  one  size  are  sometimes  present.  The  dentine 
of  the  basal  part  of  the  larger  teeth  is  in  some  genera  very 
greatly  folded,  causing  the  structure  to  be  highly  complicated. 
These  folds,  the  intervals  between  which  are  filled  with  cement, 

1  0.  Hertwig.     Ueber  das  Zahnsystem  der  Amphibien.     Arch.  mikr. 
Anat.  supplem.  Bd.  xi.  1875. 

-  G.  A.  Boulenger,  P.  Z.  S.  1890,  p.  664. 


170          THE  VERTEBRATE  SKELETON. 

radiate  inwards  from  the  exterior  and  outwards  from  the  large 
pulp  cavity.  The  basal  part  of  the  teeth  of  Ceratophrys 
(Anura)  has  a  similar  structure. 

ENDOSKELETON. 
VERTEBRAL  COLUMN. 

Four  regions  of  the  vertebral  column  can  generally  be 
recognised  in  Amphibia,  viz.  the  cervical,  the  trunk  or  thoraco- 
lumbar,  the  sacral  and  the  caudal  regions.  In  the  limbless 
Gymnophiona,  however,  only  three  regions,  the  cervical,  tho- 
racic, and  post-thoracic  can  be  made  out.  The  cervical  region 
is  limited  to  a  single  vertebra  which  generally  differs  from  the 
others  in  having  no  transverse  processes  or  indication  of  ribs. 
It  is  generally  called  the  atlas,  but  it  commonly  bears  a  small 
process  arising  from  the  anterior  face  of  the  centrum  which 
resembles  the  odontoid  process  of  higher  animals,  and  renders 
it  probable  that  the  first  vertebra  of  Amphibia  corresponds 
to  the  axis,  not  to  the  atlas.  Amphibia  generally  have  a 
single  sacral  vertebra. 

Three  elements  go  to  make  up  the  vertebral  column  in 
Amphibia,  viz. 

1.  .  the  notochord, 

2.  the  long  vertebral  centra, 

3.  inter  vertebral  cartilage  which  forms  the  joints  between 
successive  centra. 

The  relations  which  these  three  elements  bear  to  one 
another  are  subject  to  much  variation.  The  successive  stages 
can  be  well  traced  in  the  Urodela. 

1.  The  first  stage  is  found  in  larval  Urodeles  in  general 
and  in  adult  Ichthyoidea,  and  some  Salamandrina.  In  these 
forms  the  notochord  persists  and  retains  approximately  the 
same  diameter  throughout  the  whole  length  of  the  vertebral 
column.  Bony  biconcave  centra  are  present  and  constrict  it 


THE    SKELETON   IN   AMPHIBIA.      VERTEBRAL   COLUMN.    171 

to  a  certain  extent  vertebrally,  while  intervertebrally  there  is 
a  development  of  cartilage.  The  connection  between  the  bony 
vertebrae  is  effected  mainly  by  the  expanded  notochord. 

2.  In  the  next  stage,  as  seen  in  Gyrinophilus  porphyriti- 
cus,   the  growth  of    intervertebral   cartilage  has   caused  the 
almost  complete  obliteration  of  the  notochord  intervertebrally, 
and  its  entire  disappearance  vertebrally,  i.e.  in  the  centre  of 
each  vertebra.    The  intervertebral  cartilage  now  forms  the  main 
connection  between  successive  vertebrae,  and  sometimes  cases 
are  found  whose  condition  approaches  that  of  definite  articula- 
tions.    Readily  recognisable  remains  of  the  notochord  are  still 
found  at  each  end  of  the  intervertebral  constriction. 

3.  In  the  third  stage  differentiation  and  absorption  of  the 
intervertebral  cartilage  has  given  rise  to  definitely  articulating 
opisthocoelous    vertebrae.      These   are   found   in   most  adult 
Salamandrina. 

The  transverse  processes  of  the  earlier  trunk  vertebrae 
are  divided  into  two  parts,  a  dorsal  part  which  meets  the 
tubercular  process  of  the  rib  and  is  derived  from  the  neural 
arch,  and  a  ventral  part  which  meets  the  capitular  process  of 
the  rib,  and  is  derived  from  the  ventral  or  haemal  arch.  In 
the  caudal  vertebrae  and  often  also  in  the  posterior  trunk 
vertebrae  the  two  processes  are  fused. 

Siren  and  Proteus,  although  they  possess  minute  posterior 
limbs,  have  no  sacral  vertebrae,  while  Cryptobranchus  lateralis 
has  two.  The  caudal  vertebrae,  except  the  first,  have  haemal 
arches  very  similar  to  the  neural  arches. 

In  Labyrinthodontia  the  centra  of  the  vertebrae  are  gene- 
rally well  ossified  biconcave  discs.  In  some  forms  however,  like 
Euchirosaurus,  the  centra  are  imperfectly  ossified,  and  consist 
of  bony  rings  traversed  by  a  wide  notochord al  canal.  Each 
ring  is  formed  of  four  pieces,  a  large  well-ossified  neural  arch, 
a  basal  piece,  and  a  pair  of  lateral  pieces.  Vertebrae  of  this 
type  are  called  rachitomous. 


172  THE  VERTEBRATE  SKELETON. 

In  the  tail  region  of  other  forms  each  vertebra  consists 
of  an  anterior  centrum  bearing  the  neural  arch,  and  a  pos- 
terior intercentrum1  bearing  chevron  bones.  Vertebrae  of  this 
type  are  called  embolomerous.  Haemal  arches  similar  to  the 
neural  arches  are  often  found  as  in  Urodela.  The  transverse 
processes  are  sometimes  well  developed  and  are  divided  into 
tubercular  and  capitular  portions. 

In  Gymnophiona  the  vertebrae  are  biconcave  and  are  very 
numerous,  they  sometimes  number  about  two  hundred  and 
thirty.  Only  quite  the  last  few  are  ribless  and  so  can  be 
regarded  as  post-thoracic  vertebrae.  The  first  vertebra  has 
nothing  of  the  nature  of  an  odontoid  process. 

In  Anura  the  number  of  vertebrae  is  very  greatly  reduced, 
only  nine  and  the  urostyle  being  present.  Of  these,  eight  are 
presacral  and  one  sacral.  The  urostyle  is  postsacral  and 
corresponds  to  three  or  more  modified  vertebrae.  The  first 
vertebra  is  without  transverse  processes,  the  remaining  pre- 
sacral vertebrae  have  the  transverse  processes  fairly  large, 
while  the  sacral  vertebra  has  them  very  large,  forming  in 
some  genera  widely  expanded  plates.  The  urostyle  is  a  long 
cylindrical  rod  which  articulates  with  the  sacrum  generally  by 
two  facets.  Ankylosed  to  its  anterior  end  are  the  remains 
of  two  neural  arches. 

In  Anura  remains  of  the  notochord  are  found  in  the  centre 
of  each  vertebra,  i.e.  vertebrally,  while  in  the  Urodela  they 
only  occur  intervertebrally. 

The  vertebrae  in  Anura  are,  as  a  rule,  procoelous.  The 
eighth  vertebra  is  however  generally  amphicoelous,  while 
the  ninth  commonly  has  one  convexity  in  front,  and  two 
behind. 

In  some  forms  such  as  Bombinator,  Pipa,  Liscoglossus  and 
Alytes  they  are  opisthocoelous ;  in  others  like  Pelobates  they 
are  variable. 

1  See  p.  14. 


THE   SKELETON   IN    AMPHIBIA.      THE    SKULL.          173 

THE  SKULL'. 

CRANIUM  AND  MANDIBLE. 

In  the  Amphibian  skull  there  are  as  a  rule  far  fewer  bones 
than  in  the  skull  of  bony  fish.  The  primordial  cartilaginous 
cranium  often  persists  to  a  great  extent.  Only  quite  a  few 
ossifications  take  place  in  it ;  namely  in  the  occipital  region — 
the  exoccipitals,  further  forwards — the  pro-otics,  and  at  the 
boundary  of  the  orbital  and  ethmoidal  regions — the  sphen- 
ethmoid.  The  basi-occipital  and  basisphenoid  are  never 
ossified.  As  in  Mammalia  there  are  two  occipital  condyles 
formed  by  the  exoccipitals. 

Large  vacuities  commonly  occur  in  the  cartilage  of  both 
floor  and  roof  of  the  primordial  cranium.  These  are  roofed 
over  to  a  greater  or  less  extent  by  the  development  of  mem- 
brane bone.  Thus  on  the  roof  of  the  cranium  there  are  paired 
parietals,  frontals,  and  nasals,  and  on  its  floor  are  paired 
vomers,  and  a  median  unpaired  parasphenoid. 

In  all  living  forms  the  parietals  meet  and  there  is  no 
interparietal  foramen,  though  this  exists  in  Labyrintho- 
donts. 

The  palato-pterygo-quadrate  bar  is  united  at  each  end  with 
the  cranium,  but  elsewhere  in  most  cases  forms  a  wide  arch 
standing  away  from  it.  The  suspensorium  is,  as  in  Dipnoi 
and  Holocephali,  autostylic.  The  palato-pterygo-quadrate  bar 
sometimes  remains  entirely  cartilaginous,  sometimes  its  pos- 
terior half  is  ossified  forming  the  quadrate.  In  connection 
with  it  a  number  of  membrane  bones  are  generally  developed, 
viz.  the  maxillae,  premaxillae,  palatines,  pterygoids,  quadrato- 
jugals,  and  squamosals.  The  pterygoids  are,  however,  some- 
times partially  formed  by  the  ossification  of  cartilage.  The 

1  See  many  papers  by  W.  K.  Parker  published  in  the  Phil.  Trans,  of 
the  Koyal  Soc. 


174          THE  VERTEBRATE  SKELETON. 

cartilage  of  the  lower  jaw  and  its  investing  membrane  bones 
generally  have  much  the  same  relations  as  in  bony  fishes. 

URODELA.  The  skulls  of  the  various  Urodeles  show  an 
interesting  series  of  modifications  and  differ  much  from  one 
another,  but  all  agree  in  the  absence  of  the  quadratojugals, 
in  the  fact  that  the  palatines  lie  parallel  to  the  axis  of  the 
cranium,  and  in  the  large  size  of  the  parasphenoid. 

The  lower  types  Menobranchus,  Siren,  Proteus,  and  Am- 
phiuma  have  longer  and  narrower  skulls  than  do  the  higher 
types. 

Menobranchus  has  a  very  low  type  of  skull  which  remains 
throughout  life  in  much  the  same  condition  as  that  of  a  young 
tadpole  or  larval  salamander.  The  roof  and  floor  of  the 
cranium  internal  to  the  membrane  bones  are  formed  of  fibrous 
tissue,  not  of  well-developed  cartilage.  The  epi-otic  regions  of 
the  skull  are  ossified,  forming  a  pair  of  large  bones  which  lie 
external  to,  and  distinct  from,  the  exoccipitals.  Proteus  and 
the  Labyrinthodonts  are  the  only  other  Amphibia  which  have 
these  elements  separately  ossified.  The  parietals  send  a  pair 
of  long  processes  forwards  along  the  sides  of  the  frontals. 
Nasals  and  maxillae  are  absent,  as  is  likewise  the  case  in 
Proteus.  Teeth  are  borne  on  the  vomers,  premaxillae,  ptery- 
goids,  dentaries  and  angulo-splenials.  The  suspensorium  is 
forwardly  directed. 

The  skull  of  Siren  resembles  that  of  Menobranchus  in 
several  respects,  as  in  the  forward  direction  of  the  suspen- 
sorium and  in  the  absence  of  maxillae,  but  differs  in  the 
possession  of  nasals,  in  the  toothless  condition  of  the  pre- 
maxillae and  dentaries,  and  in  the  fusion  and  dentigerous  con- 
dition of  the  vomers  arid  palatines. 

Amphiuma  has  a  skull  which,  though  narrow  and  elongated, 
differs  from  those  of  Menobranchus,  Proteus,  and  Siren,  and 
resembles  those  of  higher  types  in  the  following  respects  : — 

(1)     the  suspensorium  projects  nearly  at  right  angles  to 


THE   SKELETON   IN   AMPHIBIA.      THE    SKULL.         175 

the  cranium  instead  of  being  directed  forwards,  (2)  the 
maxillae  are  well  developed,  and  the  premaxillae  are  com- 
pletely ankylosed  together,  (3)  there  are  no  palatines. 

The  skulls  of  Megalobatrachiis,  Cryptobranchus  and  Siredon 
resemble  those  of  the  highest  Urodeles  the  Salamanders  in  their 
wide  form,  in  having  the  pro-otics  distinct  from  the  exoccipitals 
which  are  ossified  continuously  with  the  epi-otics  and  opisth- 
otics,  and  in  having  no  palatines,  but  differ  in  having  the  two 
premaxillae  separate,  and  in  the  arrangement  of  the  vomerine 
teeth  which  in  Megalobatrachus  and  Cryptobranchus  are  placed 
along  the  anterior  boundaries  of  the  bones,  these  meeting  in 
the  middle  line.  In  Siredon  the  vomers  are  separated  by  the 
very  large  parasphenoid. 

The  suspensorium  in  Megalobatrachus  and  Cryptobranchus 
projects  at  right  angles  to  the  cranium ;  in  Siredon  it  projects 
somewhat  downwards  and  forwards  as  in  the  Salamandrina. 

Modifications  of  the  vomers,  pterygoids  and  palatines  ac- 
company the  changes  of  the  larval  ichthyoid  Siredon  into  the 
adult  salamandroid  Amblystoma,  the  vomers  especially  come 
to  resemble  to  a  much  greater  extent  those  of  the  Sala- 
mandrina. 

The  ossification  of  the  skull  in  the  Salamandrina  is  carried 
further  than  in  the  Ichthyoidea,4though  the  supra-occipital  and 
basi-occipital  are  not  ossified.  The  skull  differs  from  that  in 
the  Ichthyoidea  in  the  size  of  the  part  of  the  vomero-palatines 
which  lies  in  front  of  the  teeth,  in  the  frequent  union  of  the 
two  premaxillae  and  in  the  ossification  of  all  the  periotic  bones 
continuously  with  the  exoccipital. 

The  skull  differs  from  that  of  Anura  in  the  following 
respects : — 

(1)  the  bones  of  the  upper  jaw  do  not  form  a  complete 
arch  standing  away  from  the  cranium,  and  the  maxillae  are 
not  united  to  the  quadrates  by  quadratojugals,  (2)  the  long 
axis  of  the  suspensorium  passes  obliquely  downwards  and 
forwards  instead  of  downwards  and  backwards,  (3)  there  is  no 


176 


THE  VERTEBRATE  SKELETON. 


sphenethmoid  encircling  the  anterior  end  of  the  brain,  its  place 
being  partly  taken  by  a  pair  of  orbitosphenoids,  (4)  there  is  no 
definite  tympanic  cavity. 


20' 


21 


FIG.  27. 


10. 
11. 


DOKSAL   VIEW    OF    THE    SKULL    OF   A    LiABYBINTHODONT    (CupitO- 

saurus  nasutus)x%  (from  VON  ZITTEL). 

premaxilla.  12.     postorbital. 

nasal.  13. 

maxilla.  14. 

anterior  nares.  15. 

frontal.  16. 

prefrontal.  17. 

lachrymal.  18. 

jugal.  19. 

orbit.  .                 20. 

parietal.  21. 
postfrontal. 


interparietal  foramen. 

squamosal. 

supratemporal. 

quadrato  jugal. 

quadrate. 

epi-otic. 

dermo-supra-occipital. 

exoccipital. 

foramen  magnum. 


LABYRINTHODONTIA.  The  skull  in  Labyrinthodontia  is  re- 
markable for  its  extreme  solidity,  the  large  number  of  bones 
which  are  present,  and  the  extent  to  which  the  roofing  over  of 


THE   SKELETON   IN   AMPHIBIA.      THE   SKULL.         177 

the  temporal  and  other  fossae  has  taken  place.  In  many 
forms  the  surface  of  the  bones  is  as  in  Crocodiles,  strongly 
sculptured  (fig.  27,  right  half)  with  ridges  and  grooves  which 
probably  lodged  sensory  organs.  The  bones  forming  the 
roof  of  the  skull  are  generally  very  uniform  in  size,  perhaps 
the  most  noticeable  of  them  being  the  paired  dermo-supra- 
occipitals  (fig.  27,  19).  Paired  dermo-supra-occipitals  occur 
also  in  certain  Ganoids.  The  Labyrinthodont  skull  also 
bears  resemblance  to  that  of  many  fish  in  the  development 
of  a  pair  of  long  pointed  epi-otics  (fig.  27,  18),  which  remain 
permanently  distinct  from  the  surrounding  bones.  The  pa- 
rietals  are  small  and  enclose  between  them  the  interparietal 
foramen  (fig.  27,  13).  In  some  forms  in  which  the  head  is 
protected  with  an  armour  of  scutes,  these  do  not  roof  over 
the  interparietal  foramen,  and  from  this  fact  it  has  been 
inferred  that  the  Labyrinthodonts  had  a  functional  pineal 
eye.  Both  supra-  and  infra-temporal  fossae  are  partially  or 
completely  roofed  over  by  the  postorbitals  and  large  supra- 
temporals  (fig.  27,  15). 

There  is  generally  a  ring  of  bones  in  the  sclerotic  coat 
of  the  eye.  The  pterygoids  do  not  meet  in  the  middle  line, 
being  separated  by  the  parasphenoid.  The  palatines  bear 
teeth,  and  in  some  genera  (Arckegosaurus)  form  long  splints 
lying  along  the  inner  side  of  the  maxillae  and  more  or  less 
surrounding  the  posterior  nares.  In  others  (Nyrania)  they 
lie  in  the  normal  position  near  the  middle  line,  one  on 
each  side  of  the  parasphenoid.  The  vomers  bear  teeth  and 
sometimes  meet  in  the  middle  line ;  they  are  sometimes 
confluent  with  the  parasphenoid.  On  the  ventral  surface 
of  the  cranium  there  are  generally  large  palatal  vacui- 
ties. 

In  the  mandible  there  is  often  a  well-marked  postglenoid 
process,  and  the  articular  is  generally  completely  ossified. 

GrYMNOPHioNA.  The  skull  bears  a  considerable  resemblance 
to  that  of  Labyrinthodonts,  especially  in  the  arrangement  of 
R.  12 


178 


THE  VERTEBRATE  SKELETON. 


-10 


12 


FlG.    28.       A,    VENTRAL   VIEW   OF    THE    CRANIUM  J    B,    LATERAL   VIEW    OF    THE 

CRANIUM  AND  MANDIBLE  OF  Siphonops  aimulatus  (after  WIEDERSHEIM). 


1.  anterior  nares. 

2.  naso-premaxilla. 

3.  frontal. 

4.  parietal. 

5.  maxilla. 

6.  vomer. 

7.  orbit. 

8.  quadrate    united    with 

pterygoid  in  front. 


9.  squamosal. 

10.  exoccipital. 

11.  dentary. 

12.  angular. 

13.  basi-occipital   and  basisphe- 

noid  fused. 

14.  posterior  narial  opening  sur- 
the  rounded  by  the  palatine. 

X.  pneumogastric  foramen. 


THE   SKELETON   IN   AMPHIBIA.      THE   SKULL.         179 

the  bones  which  bound  the  mouth  cavity.  The  cranium  is 
very  hard,  and  is  covered  by  a  complete  bony  roof  formed 
mainly  of  the  exoccipitals,  parietals,  frontals,  prefrontals, 
nasals  and  premaxillae.  The  nasals  and  premaxillae  are 
sometimes  ossified  continuously.  There  is  a  median  unpaired 
ethmoid  whose  dorsal  end  appears  at  the  surface  wedged  in 
between  the  frontals  and  parietals.  The  bone  generally 
regarded  as  the  squamosal1  is  very  large,  and  it  and  the 
maxilla  generally  together  surround  the  orbit,  which,  in 
.Epicrium,  has  in  it  a  ring  of  bones.  The  palatines  form  long 
tooth-bearing  bones  fused  with  the  inner  sides  of  the  maxillae; 
they  nearly  surround  the  posterior  nares. 

The  quadrate  bears  the  knob,  and  the  angular  the  cup 
for  the  articulation  of  the  mandible, — a  very  primitive  feature. 
The  mandible  is  also  noticeable  for  the  enormous  backward 
projection  of  the  angular. 

ANURA.  In  Anura  the  skull  is  very  short  and  wide 
owing  to  the  transverse  position  of  the  suspensorium.  There 
is  often  a  small  ossification  representing  the  quadrate.  Some- 
times as  in  Hyla  and  Alytes  there  is  a  fron to-parietal 
fontanelle. 

As  compared  with  the  skull  in  Urodela  the  chief  charac- 
teristics of  the  skull  of  Anura  are  : — 

1.  the  presence  of  a  sphenethmoid, 

2.  the  union  of  the  frontals  and  parietals  on  each  side, 

3.  the   occasional   occurrence   of  small  supra-  and   basi- 
occipitals, 

4.  the  backward  growth  of  the  maxilla  and  its  connection 
with  the  suspensorium  by  means  of  the  quadratojugal, 

5.  the  dagger-like  shape  of  the  parasphenoid, 

6.  the  occurrence  of  a  definite  tympanic  cavity, 

1  Perhaps  this  bone  includes  supra-orbital  and  postorbital  elements. 

12—2 


180          THE  VERTEBRATE  SKELETON. 

7.  the  frequent  occurrence  of  a  pre-dentary  or  mento- 
meckelian  ossification  in  the  mandible. 

The  skull  of  Pipa  is  abnormal,  being  greatly  flattened  and 
containing  little  cartilage.  The  fronto-parietals  are  fused,  and 
there  is  no  sphenethmoid.  The  quadrates  are  well  developed 
and  the  squamosals  and  parasphenoid  differ  much  from  those 
of  other  Anura. 

HYOID    AND    BRANCHIAL    ARCHES. 

In  larval  Amphibia  the  hyoid  and  four  branchial  arches 
are  generally  present,  and  in  adult  Ichthyoidea  they  are 
frequently  almost  as  well  represented  as  in  the  larva,  and 
are  of  use  in  strengthening  the  swallowing  apparatus.  They 
are  very  well  seen  in  Siredon,  and  consist  of  a  hyoid  attached 
by  ligaments  to  the  suspensorium,  followed  by  four  branchial 
arches  of  which  the  first  and  second  are  united  by  a  copula 
(fig.  29,  D,  8),  while  the  third  and  fourth  are  not.  The  hyoid 
is  not  always  the  largest  and  best  preserved  of  the  arches, 
for  sometimes  as  in  Spelerpes  one  of  the  branchials  is  far 
larger  than  the  hyoid.  Four  branchial  arches  occur  in  Siren 
as  in  Siredon,  but  in  Proteus  there  are  only  three. 

In  some  larval  Labyrinthodontia  (Branckiosaurus)  four 
branchial  arches  are  known  to  occur,  and  their  arrangement 
is  almost  precisely  similar  to  that  in  Siredon. 

In  Gymnophiona  the  remains  of  only  three  branchial 
arches  occur  in  addition  to  the  hyoid.  The  four  arches  are 
all  very  similar  to  one  another,  each  consists  of  a  curved  rod 
of  uniform  diameter  throughout.  The  hyoid  is  united  with 
the  first  branchial  arch,  but  has  no  attachment  to  the 
cranium. 

In  larval  Anura  (fig.  29,  C)  the  arrangement  of  the 
hyoid  and  branchial  arches  is  much  as  in  Urodela.  In  the 
adult,  however,  the  ventral  parts  of  all  the  arches  unite,  form- 
ing a  compact  structure,  the  basilingual  plate  (fig.  29,  B,  1). 


THE    SKELETON    IN   AMPHIBIA.      THE    HYOID. 


181 


The  dorsal  parts  of  the  first  three  branchial  arches  disappear, 
but  those  of  the  fourth  become  ossified  and  form  the  short, 
stout  thyrohyals  or  posterior  cornua.  The  dorsal  parts  of  the 
hyoid  arch  in  the  adult  form  a  pair  of  long  bars,  the  anterior 


FIG.  29.     VISCERAL  ARCHES  OF  AMPHIBIA. 

A.  Molge  cristata  (after  PARKER). 

B.  Rana  temporaria      adult  (after  PARKER). 

C.  Tadpole  of  Rana  (after  MARTIN  ST  ANGE). 

D.  Siredon  pisciformis  (after  CREDNER). 

In  each  case  the  ossified  portions  are  slightly  shaded,  while  the  carti- 
laginous portions  are  left  white. 


1.  basilingual  plate. 

2.  hyoid  arch. 

3.  first  branchial  arch. 

4.  second        do. 


5.  third  branchial  arch. 

6.  fourth         do. 

7.  tbyrohyal. 

8.  copula. 


18*2          THE  VERTEBRATE  SKELETON. 

cornua,  which  are  united  to  the  periotic  region  of  the  skull  iii 
front  of  the  fenestra  ovalis  either  by  short  ligaments  or  by 
fusion  as  in  Bufo.  In  Pipa  and  Xenopus  the  first  and 
second  branchial  arches  persist  as  well  as  the  fourth  (thyro- 
hyal),  but  in  Pipa  the  hyoid  is  wanting. 

KIBS. 

Ribs  are  generally  very  poorly  developed  in  Amphibia. 
In  Anura  they  are  in  most  cases  absent;  when  present  they 
generally  form  minute  unossified  appendages  attached  to  the 
transverse  processes,  but  in  Discoglossus  and  Xenopus  the 
anterior  vertebrae  are  provided  with  distinct  ribs.  In 
Urodela  and  Labyrinthodontia  they  are  generally  short 
structures,  each  as  a  rule  attached  to  the  vertebra  by  a 
bifurcated  proximal  end.  The  number  of  rib-bearing  vertebrae 
varies,  but  the  first  and  the  posterior  caudal  vertebrae  are 
always  ribless.  The  anterior  caudal  vertebrae  too  are  gene- 
rally ribless,  but  sometimes  a  few  of  them  bear  small  ribs. 
In  Spelerpes  the  last  two  trunk  vertebrae  are  ribless,  and 
hence  may  be  regarded  as  lumbar  vertebrae. 

In  Gymnophiona  ribs  are  better  developed  than  in  any 
other  Amphibia;  they  occur  on  all  the  vertebrae  except  the 
first  and  last  few,  and  are  attached  to  the  transverse  processes, 
sometimes  by  single,  sometimes  by  double  heads. 

Sternal  ribs  are  almost  unknown  in  Amphibia,  but  traces 
of  them  occur  in  Menobranclius. 

STERNUM. 

In  Amphibia  the  sternum  is  not  very  well  developed; 
sometimes  as  in  Gymnophiona  and  Proteus  no  traces  of  it 
occur,  and  in  the  Urodela  it  is  never  ossified.  It  is  always 
very  intimately  related  to  the  pectoral  girdle.  In  the  Sala- 
mandrina  it  has  the  form  of  a  broad  thin  plate  of  cartilage, 
grooved  and  overlapped  by  the  coracoid. 

In  most  Anura  the  sternum  consists  of  a  number  of  parts 


THE    SKELETON    IN    AMPHIBIA.      THE    STERNUM.      183 

A 


FIG.  30.     SHOULDER-GIRDLE  AND  STERNUM  OF 

A.  An  old  male  common  Frog  (Eana  temporaria). 

B.  An  adult  female  Docidophryne  gigantea  (after  PARKER). 

In  both  A  and  B  the  left  suprascapula  is  removed.  The  parts  left 
unshaded  are  ossified ;  those  marked  with  small  dots  consist  of  hyaline 
cartilage,  those  marked  with  large  dots  of  calcified  cartilage. 

1.  calcified  cartilage  of  supra-  7.     clavicle. 

scapula.  8.     glenoid  cavity. 

2.  ossified    portion    of    supra-  9.     coracoid  foramen. 

scapula.  10.  episternum. 

3.  scapula.  11.  omosternum. 

4.  coracoid.  12.  sternum. 

5.  epicoracoid.  13.  xiphisternum. 

6.  precoracoid. 


184          THE  VERTEBRATE  SKELETON. 

arranged  in  series.  At  the  anterior  end  is  a  flat  cartilaginous 
plate  with  a  bony  basal  stalk.  This  plate  is  called  the  epi- 
stermim,  and  its  stalk  the  omosternum.  The  continuity  of 
the  sternum  is  now  interrupted  by  a  pair  of  cartilaginous 
structures,  the  epicoracoids,  which  are  shoulder-girdle  elements, 
and  represent  the  unossified  ventral  ends  of  the  coracoids.  In 
some  cases  cartilaginous  epiprecoracoids  can  also  be  distin- 
guished. Further  back  is  the  long  sternum  proper,  while  last 
comes  the  xiphisternum,  a  broad  expanded  plate  of  cartilage. 

In  some  Anura  such  as  Pipa  and  Hyla  the  number  of 
sternal  elements  is  considerably  reduced. 

APPENDICULAR  SKELETON. 
PECTORAL  GIRDLE. 

The  most  primitive  Amphibian  shoulder-girdle  is  found  in 
the  Urodela.  It  consists  of  a  dorsal  element,  the  scapula, 
a  posterior  ventral  element,  the  coracoid,  and  an  anterior 
ventral  element,  the  precoracoid.  The  clavicle  is  not  de- 
veloped, and  the  two  coracoids  overlap  in  the  middle  line. 
The  shoulder-girdle  remains  largely  cartilaginous  but  the 
proximal  end  of  the  scapula  is  ossified,  and  the  ossification 
may  extend  through  part  of  the  coracoid  and  precoracoid. 

In  Labyrinthodontia  there  is  an  exoskeletal  ventral  buckler 
formed  of  three  plates,  a  median  one,  which  probably  repre- 
sents an  interclavicle,  and  two  lateral  ones,  which  are  probably 
clavicles.  Traces  of  endoskeletal  structures,  probably  corre- 
sponding to  the  precoracoid  and  scapula,  are  also  known  in 
some  cases.  The  Gymnophiona  and  some  of  the  Labyrintho- 
dontia have  lost  the  pectoral  girdle  and  limbs. 

The  ossification  of  the  shoulder-girdle  has  gone  on  much 
further  in  Anura  than  it  has  in  Urodela.  Clavicles  are  present 
and  the  scapula  and  coracoid  of  each  side  are  ossified  from 
separate  centres.  The  distal  part  of  the  scapula  forms  a  large 
imperfectly  ossified  plate,  the  suprascapula. 


THE   SKELETON    IN    AMPHIBIA.      ANTERIOR   LIMB.      185 

The  shoulder-girdle  of  Anura  is  however  subject  to  con- 
siderable variations.  In  the  Toads  (Bufonidae)  the  epicora- 
coids  or  unossified  ventral  ends  of  the  coracoids  and  pre- 
coracoids  overlap  in  the  middle  line  (fig.  30,  B,  5).  This 
arrangement  is  called  Arciferous.  In  the  Frogs, — Ranidae, 
and  other  forms  belonging  to  the  group  Firmisternia, — the 
epicoracoids  do  not  overlap  but  form  a  narrow  cartilaginous 
bar  separating  the  ventral  ends  of  the  coracoids  (fig.  30,  A,  5). 

ANTERIOR  LIMB. 

In  many  Amphibia  and  especially  in  the  Urodela  the 
anterior  limb  has  a  very  simple  unmodified  arrangement. 
The  humerus  is  straight  and  of  moderate  length,  its  ends  are 
rounded  for  articulation  on  the  one  hand  with  the  shoulder- 
girdle,  and  on  the  other  hand  with  the  radius  and  ulna.  In 
the  Urodela  the  radius  and  ulna  are  distinct.  In  the  Anura 
they  have  fused,  though  the  line  of  junction  of  the  two 
is  not  obliterated.  Their  proximal  ends  are  hollowed  for 
articulation  with  the  convex  end  of  the  humerus. 

The  manus  in  all  recent  Amphibia  agrees  in  never  having 
more  than  four  complete  digits,  but  is  subject  to  considerable 
variation,  this  statement  applying  especially  to  the  carpus. 

In  the  larva  of  Salamandra  (fig.  31,  A),  except  that  the 
pollex  is  absent1,  the  inanus  retains  completely  the  condition 
which  is  generally  regarded  as  primitive  for  the  higher 
Vertebrata.  It  consists  of  an  anterior  row  of  three  elements, 
the  ulnare,  intermedium,  and  radiale,  and  a  posterior  row 
of  four,  the  carpalia  2,  3,  4,  and  5.  Interposed  between  the 
two  rows  is  a  centrale.  Menobranclius  has  a  similar  very 
simple  carpus.  In  most  other  Amphibia  this  simplicity  is 
lost.  This  loss  may  be  due  to  : — 

(a)  fusion  of  certain  structures,  e.g.  in  the  adult  Sala- 
mandra the  intermedium  and  ulnare  have  fused, 

1  The  first  digit  present  is  sometimes  regarded  as  the  pollex,  but  from 
analogy  with  Anura  it  is  probable  that  tbe  pollex  is  the  missing  digit. 


186 


THE  VERTEBRATE  SKELETON. 


(b)  displacement  of  structures,   e.g.  in  Bufo  viridis,  the 
centrale   has  been  pushed  up  till  it  comes  to  articulate  with 
the  radius, 

(c)  the  development  of  supernumerary  elements,  especially 
of  extra  centralia.     In    Megalobatrachus   two  or   even  three 
centralia  sometimes  occur. 


FIG.  31.     A,  EIGHT   ANTIBRACHIUM   AND    MANUS  OF  A  LARVAL  SALAMAN- 
DER (Salamandra  maculosa)  (after  GEGENBAUR). 
B,  EIGHT  TARSUS   AND  ADJOINING  BONES  OF  Molge  sp.   (after 
GEGENBAUR). 

1.  radius.  11.     tibia. 

2.  ulna.  12.     fibula. 

3.  radiale.  13.    tibiale. 

4.  intermedium. 

5.  ulnare. 

6.  centrale. 

7.  carpale  2. 

8.  3. 


14.  intermedium. 

15.  fibulare. 

16.  centrale. 

17.  tarsale  1. 

18.  tarsalia  4  and  5  fused. 


9. 
10. 


I.  II.  III.  IV.  V.  digits. 


In  the  great  majority  of  Amphibia  while  one  digit, 
probably  the  first,  is  absent,  the  other  four  digits  are  well 
developed.  In  the  forms  however  with  degenerate  limbs  like 
Amphiuma,  Siren  and  Proteus  the  number  of  digits  is  still 


THE   SKELETON   IN   AMPHIBIA.      PELVIC   GIRDLE.     187 

further  reduced.  In  Siren  there  are  three  or  four,  in  Proteus 
three,  and  in  Amphiuma  two  or  three  digits  in  the  manus. 

In  Anura  the  pollex  is  represented  only  by  a  short 
metacarpal.  There  are  sometimes  traces  of  a  pre-pollex. 
The  carpus  often  has  two  centralia  and  the  intermedium 
is  absent. 

In  Labyrinthodontia  the  limbs  are  generally  very  simple 
and  resemble  those  of  Urodela.  In  some  forms,  however,  the 
manus  differs  from  that  of  all  living  Amphibia  in  possessing 
five  well-developed  digits. 

PELVIC  GIRDLE. 

The  simplest  Amphibian  pelvis  is  that  of  some  of  the 
Labyrinthodontia;  thus  in  Mastodonsaurus  it  consists  dorsally 
of  a  short  broad  ilium  placed  vertically  and  attached  to  the 
sacrum,  and  ventrally  of  a  small  pubis  and  of  a  large 
ischium  meeting  its  fellow  in  the  middle  line.  In  some 
Labyrinthodonts  the  pubes  as  well  as  the  ischia  meet  in 
a  ventral  symphysis,  and  in  many  there  are  no  obturator 
foramina.  In  Siren,  Gymnophiona  and  some  Labyrinthodontia 
the  pelvic  girdle  and  limbs  are  absent. 

In  Urodela  the  ventral  element  of  the  pelvis  on  each  side 
forms  a  flat  plate  which  meets  its  fellow  of  the  opposite  side. 
The  anterior  part  of  the  plate,  representing  the  pubis,  gene- 
rally remains  cartilaginous  throughout  life ;  the  posterior 
part  representing  the  ischium  is  in  almost  every  case  well 
ossified.  Attached  to  the  anterior  end  of  the  pubes  there  is 
an  unpaired  bifid  cartilaginous  structure,  the  epipubis.  The 
ilia  are  vertically  placed. 

In  most  Anura  the  pelvis  is  peculiarly  modified  in  corre- 
lation with  the  habits  of  jumping.  The  long  bone  generally 
called  the  ilium  is  placed  horizontally  and  is  attached  at  its 
extreme  anterior  end  to  the  sacrum.  The  ischium  is  ossified 
and  distinct.  Ventrally  in  front  of  the  ischium  there  is  a 
tract  of  unossified  cartilage  which  is  often  regarded  as  the 


188          THE  VERTEBRATE  SKELETON. 

pubis.  In  Xenopus,  however,  the  bone  corresponding  to  the 
ilium  of  the  Frog  is  seen  to  ossify  from  two  centres,  one 
forming  the  ilium,  the  other,  which  lies  at  the  symphysis, 
being  apparently  the  pubis.  This  makes  it  probable  that  the 
so-called  ilium  of  the  Frog  is  really  to  be  regarded  as  an  ilio- 
pubis,  and  renders  the  homology  of  the  cartilaginous  part 
uncertain,  but  it  probably  corresponds  to  the  acetabular  bone 
of  mammals.  In  Xenopus  also  there  is  a  minute  epipubis 
similar  to  that  of  Urodeles. 

POSTERIOR  LIMB. 

In  Urodela  the  posterior  limb  (fig.  31,  B)  closely  resembles 
the  anterior  limb,  but  is  even  less  removed  from  the  primitive 
condition  of  the  higher  vertebrates  in  the  fact  that  all  five  digits 
are  commonly  present.  The  tibia  and  fibula  are  short  bones 
approximately  equal  in  size.  In  some  cases  the  number  of 
digits  is  reduced.  Thus  in  Menobranchus  the  pes  has  four 
digits,  in  Proteus  it  has  two,  and  in  Amphiuma  two  or  three, 
while  in  Siren  the  posterior  limbs  have  atrophied. 

In  correlation  with  their  habits  of  jumping,  the  posterior 
limbs  in  Anura  are  much  lengthened  and  considerably  modified. 
The  tibia  and  fibula  are  completely  fused.  The  intermedium 
is  absent,  while  the  tibiale  and  fibulare  are  greatly  elongated. 
Tarsalia  4  and  5  are  absent.  Five  digits  are  always  present, 
and  there  is  a  pre-hallux  formed  of  two  or  more  segments. 

In  general  the  posterior  limbs  in  Labyrinthodontia  bear  the 
closest  resemblance  to  the  anterior  limbs ;  in  some  cases  three 
centralia  are  found. 

In  Ichthyoidea,  and  in  most  Labyrinthodontia,  the  carti- 
lages of  the  carpus  and  tarsus  remain  unossified;  in  Salaman- 
drina  and  in  Anura  they  are  generally  ossified. 


CHAPTER  XIII. 
SAUROPSIDA. 

THIS  great  group  includes  the  Reptiles  and  Birds  and 
forms  the  second  of  the  three  into  which  the  Gnathostomata 
may  be  divided.  There  is  nearly  always  a  strongly -developed 
epiblastic  exoskeleton  which  has  the  form  of  scales  or  feathers, 
and  in  some  cases  a  dermal  exoskeleton  is  also  well  developed. 
In  living  forms  the  notochord  never  persists,  being  replaced 
by  vertebrae,  but  in  some  extinct  forms  the  centra  are 
notochordal.  The  vertebral  centra  are  ossified,  and  only  in 
exceptionally  rare  cases  have  terminal  epiphyses.  The  skull 
is  well  ossified  and  has  membrane  bones  incorporated  in  its 
walls. 

The  occipital  segment  is  completely  ossified,  and  an  inter- 
orbital  septum  or  bony  partition  separating  the  two  orbits 
is  usually  developed  to  a  greater  or  less  extent.  The  skull 
generally  articulates  with  the  vertebral  column  by  a  single 
occipital  condyle  into  the  composition  of  which  the  ex- 
occipitals  and  basi-occipital  enter  in  varying  proportions. 
The  pro-otic  ossifies,  and  either  remains  distinct  from  the 
epi-otic1  and  opisthotic  throughout  life,  or  unites  with  them 
only  after  they  have  fused  with  the  adjacent  bones.  The 
hyoid  and  branchial  arches  are  much  reduced ;  and  the 
representative  of  the  hyomandibular  is  connected  with  the 

1  According  to  Baur  a  distinct  epi-otic  is  not  recognisable  in  the 
reptilian  skull. 


190  THE  VERTEBRATE  SKELETON. 

auditory  apparatus,  forming  the  auditory  ossicles1.  Each 
ramus  of  the  mandible  always  consists  of  a  cartilage  bone, 
the  articular,  and  several  membrane  bones.  The  mandible 
articulates  with  the  cranium  by  means  of  a  quadrate.  The 
ribs  in  Birds  and  some  Reptiles  bear  uncinate  processes,  i.e. 
small,  flat,  bony  or  cartilaginous  plates  projecting  backwards 
from  their  posterior  borders.  The  sternum  is  not  transversely 
segmented  as  in  mammals,  and  there  are  commonly  distinct 
cervical  ribs.  The  ankle  joint  is  intertarsal,  or  situated 
between  the  proximal  and  distal  row  of  tarsal  bones,  not 
crurotarsal  as  in  Mammalia. 


CLASS  I. 

The  axial  skeleton  is  generally  long,  and  that  of  the  limbs 
frequently  comparatively  short,  or  sometimes  absent. 

The  exoskeleton  generally  has  the  form  of  epidermal 
scales,  which  are  often  combined  with  underlying  bony  dermal 
plates  or  scutes  and  may  sometimes  form  a  continuous  armour. 
Neither  feathers  nor  true  hairs  are  ever  present.  The  verte- 
bral column  is  generally  divisible  into  the  five  usual  regions. 
The  centra  of  the  vertebrae  vary  enormously,  and  may  be 
amphicoelous,  procoelous,  opisthocoelous  or  flat,  but  they  never 
have  saddle-shaped  articulating  surfaces.  The  quadrate  is 
always  large,  and  is  sometimes  fixed,  sometimes  movable. 
A  transpalatine  bone  uniting  the  pterygoid  and  maxilla  is 
generally  present. 

Free  ribs  are  often  borne  along  almost  the  whole  length 
of  the  trunk  and  tail,  and  often  occur  attached  to  the  cervical 
vertebrae.  The  sacrum  is  generally  composed  of  two  vertebrae 
which  are  united  with  the  ilia  by  means  of  expanded  ribs. 
The  sternum  is  rhomboidal,  and  may  either  be  cartilaginous 

1  H.  Gadow,  Phil.  Trans.,  vol.  179,  1888. 

2  See  G.  Baur,  J.  Morph.,  vol.  i.,  1887.     K.  Lydekker,  Catalogue  of 
the  Fossil  Reptilia  and  Amphibia  in  the  British  Museum,  Parts  i.  &  u. 
C.  K.  Hoffmann,  Reptilien,  in  Bronn's  Classen  und  Ordnungen  des  Thier- 
reichs,  Bd.  vi.,  3  abth.  1879—90. 


REPTILIA.      THEROMORPHA.  191 

or  formed  of  cartilage  bone,  but  never  of  membrane  bone ; 
it  differs  from  that  of  birds  also  in  the  fact  that  it  does  not 
ossify  from  two  or  more  centres.  An  interclavicle  is  generally 
present.  There  are  always  more  than  three  digits  in  the 
manus,  and  never  less  than  three  in  the  pes.  In  all  living 
reptiles  the  ilia  are  prolonged  further  behind  the  acetabula 
than  in  front  of  them,  and  the  bones  of  the  pelvis  remain  as 
a  rule,  distinct  from  one  another  throughout  life. 

The  pubes  (pre-pubes)  and  ischia  both  commonly  meet  in 
ventral  symphysis,  and  the  acetabula  are  wholly  or  almost 
wholly  ossified.  The  metatarsals  are  not  ankylosed  together. 

Order  1.     THEROMORPHA '. 

This  order  includes  a  number  of  mainly  terrestrial,  extinct 
reptiles,  which  differ  much  from  one  another,  and  show  remark- 
able points  of  affinit}r  on  the  one  hand  with  the  Labyrintho- 
dont  Amphibia,  and  on  the  other  with  the  Mammalia.  The 
vertebrae  are  nearly  always  amphicoelous  and  sometimes  have 
notochordal  centra.  The  skull  is  short  and  has  the  quadrate 
immovably  fixed.  There  is  an  interparietal  foramen,  and  gene- 
rally large  supratemporal  fossae  bounded  by  supratemporal 2 
arcades,  but  with  no  infratemporal2  arcades;  Elginia  however 
has  the  whole  of  the  temporal  region  completely  roofed  over. 

The  teeth  are  placed  in  distinct  sockets  and  are  very 
variable  in  form,  the  dentition  sometimes  resembling  the 
heterodont  dentition  of  mammals.  The  humerus  has  distinct 
condyles  and  an  ent-epicondylar  foramen3  as  in  many  mammals. 

The  pubis  is  fused  with  the  ischium,  and  both  pectoral  and 
pelvic  girdles  are  remarkably  solid.  The  obturator  foramen 

1  T.  H.  Huxley,  Quart.  J.  Geol  Soc.,  vol.  xv.  p.  649,  1859.    R.  Owen, 
Catalogue  of  Fossil  Reptiles  of  S.  Africa  in  the  British  Museum,  London, 
1876.     H.  G.  Seeley,  various  papers  published  in  the  P.  R.  Soc.  London, 
and  Phil.  Trans. 

2  See  pp.  281—283. 

3  An  ent-epicondylar  foramen  is  one  piercing  the  humerus  on  its 
inner  side  just  above  the  condyle. 


192          THE  VERTEBRATE  SKELETON. 

is  remarkably  small  or  even  absent.  The  anterior  ribs  have 
two  articulating  surfaces,  and  each  articulates  by  its  tuber- 
culum  with  the  transverse  process,  and  by  its  capitulum  with 
the  centrum  as  in  mammals. 

These  reptiles  occur  chiefly  in  deposits  of  Triassic  and 
Permian  age.  Some  of  the  best  known  genera  are  Dicynodon, 
Udenodon,  Placodus,  Pariasaurus  and  Galesaurus.  They  will 
be  noticed  in  the  general  account  of  the  skeleton  in  reptiles. 

Order  2.     SAUROPTERYGIA. 

This  order  includes  a  number  of  extinct  marine  reptiles, 
devoid  of  an  exoskeleton.  The  tail  is  short,  the  trunk  long, 
and  the  neck  in  the  most  typical  forms  extremely  long.  The 
vertebrae  have  slightly  biconcave,  or  nearly  flat  centra.  The 
skull  is  relatively  small  and  has  large  supratemporal  fossae. 
The  teeth  are  placed  in  distinct  sockets,  and  are  generally 
confined  to  the  margins  of  the  jaws ;  they  are  sharp  and 
curved  and  are  coated  with  grooved  enamel.  The  premaxillae 
are  large,  and  there  is  an  interparietal  foramen.  The  quadrate 
is  firmly  united  to  the  cranium.  The  anterior  nares  are 
separate  and  are  placed  somewhat  close  to  the  orbits.  There 
is  no  ossified  sclerotic  ring.  The  palatines  and  pterygoids 
meet  the  vomers,  and  more  or  less  completely  close  the  palate, 
and  in  some  forms,  e.g.  Plesiosaurus,  there  is  a  distinct  para- 
sphenoid.  Thoracic  ribs  are  strongly  developed  and  each 
articulates  with  its  vertebra  by  a  single  head.  The  cervical 
vertebrae  have  well-marked  ribs,  which  articulate  only  with 
the  centra,  in  this  respect  differing  from  those  of  Crocodiles. 
The  caudal  vertebrae  bear  both  ribs  and  chevron  bones,  and 
abdominal  splint-ribs  are  largely  developed. 

In  the  shoulder-girdle  the  coracoids  are  large  and  meet  in  a 
ventral  symphysis  ;  precoracoids  and  a  sternum  are  apparently 
absent,  but  parts  generally  regarded1  as  the  clavicles  and 

1  According  to  Hulke  they  should  be  regarded  as  the  omosternum, — 
the  clavicles  and  interclavicle  being  wanting. 


REPTILIA.      CHELONIA.  193 

interclavicle  are  well  developed.  In  the  pelvis,  the  pubes  and 
ischia  meet  in  a  long  symphysis.  The  limbs  are  pentedactylate, 
and  in  the  best  known  forms,  the  Plesiosauridae,  form  swim- 
ming paddles. 

The  Sauropterygia  occur  in  beds  of  Secondary  age,  and 
some  of  the  best  known  genera  are  Plesiosaurus,  Pliosaurus 
and  Nothosaurus. 


Order  3.     CHELOXIA. 

In  the  Tortoises  and  Turtles  the  body  is  enclosed  in  a  bony 
box,  formed  of  the  dorsal  carapace,  and  a  flat  ventral  buckler, 
the  plastron.  Except  in  Dermochelys  the  carapace  is  partly 
formed  from  the  vertebral  column  and  ribs,  partly  from  dermal 
bones.  Both  carapace  and  plastron  are,  except  in  Dermo- 
chelys, Trionyx  and  their  allies,  covered  with  an  epidermal 
exoskeleton  of  horny  plates,  which  are  regularly  arranged, 
though  their  outlines  do  not  coincide  with  those  of  the  under- 
lying bones.  The  thoracic  vertebrae  have  no  transverse  pro- 
cesses, and  are  quite  immovably  fixed,  but  the  cervical  and 
caudal  vertebrae  are  very  freely  movable.  There  are  no  lumbar 
vertebrae.  The  skull  is  extremely  solid,  and  frequently  has  a 
very  complete  false  roof.  Teeth  have  been  detected  in  embryos 
of  Trionyx  but  with  this  exception  the  jaws  are  toothless, 
and  are  encased  in  horny  beaks.  The  quadrate  is  firmly 
fixed.  The  facial  part  of  the  skull  is  very  short,  and  the 
alisphenoidal  and  orbitosphenoidal  regions  are  unossified.  In 
living  forms  there  are  no  separate  nasal  bones,  while  large 
pref rentals  and  postfrontals  are  developed.  There  is  a  com- 
paratively complete  bony  palate  chiefly  formed  of  the  palatines 
and  pterygoids.  The  anterior  nares  are  united  and  placed  at 
the  anterior  end  of  the  skull,  and  the  premaxillae  are  very 
small.  There  is  no  transpalatine  bone  and  the  vomer  is 
unpaired.  The  dentaries  are  generally  fused  together. 

There  are  ten  pairs  of  ribs,  and  each  rib  has  only  a  single 
R.  13 


194          THE  VERTEBRATE  SKELETON. 

head  and  is  partially  attached  to  two  vertebrae ;  there  are  no 
cervical  or  sternal  ribs.  There  is  no  true  sternum. 

The  three  anterior  elements  of  the  plastron  are  respectively 
homologous  with  the  interclavicle  and  two  clavicles  of  other 
reptiles,  while  the  remaining  elements  of  the  plastron  are  pro- 
bably homologous  with  the  abdominal  ribs  of  Crocodiles.  The 
pectoral  girdle  lies  within  the  ribs,  and  the  precoracoids  and 
coracoids  do  not  meet  in  ventral  symphyses.  The  scapula  and 
precoracoid  are  ossified  continuously.  The  pubis  probably 
corresponds  with  the  prepubis  of  Dinosaurs.  There  are  four 
limbs  each  with  five  digits. 

The  order  includes  three  suborders  : — 

Suborder  (1).     TRIONYCHIA. 

The  carapace  and  plastron  have  a  rough  granular  surface 
covered  with  skin  and  without  any  horny  shields. 

The  plastron  is  imperfectly  ossified,  and  marginal  bones 
may  be  absent,  or  if  present  are  confined  to  the  posterior 
portion  of  the  carapace.  The  pelvis  is  not  united  to  the 
plastron.  The  cranium  has  not  a  complete  false  roof  and  the 
head  can  be  drawn  back  under  the  carapace. 

The  first  three  digits  of  both  manus  and  pes  bear  claws, 
and  the  fourth  digit  in  each  case  has  more  than  three  pha- 
langes. The  most  important  genus  is  Tribnyx. 

Suborder  (2).     CRYPTODIRA. 

The  carapace  and  plastron  vary  in  the  extent  to  which  they 
are  ossified,  and  except  in  Dermochelys1  and  its  allies  are 
covered  by  horny  plates.  Marginal  bones  are  always  present. 
The  head  can  generally  be  drawn  back  under  the  carapace. 
The  pelvis  is  not  firmly  united  to  the  plastron.  The  cranium 
often  has  a  complete  false  roof,  and  in  the  mandibular  articu- 
lation the  cup  is  borne  by  the  cranium,  and  the  knob  by  the 
mandible.  Among  the  more  important  genera  are  Dermo- 
chelys,  Ckelone,  and  Testudo. 

1  See  p.  272. 


REPTILIA.      ICHTHYOSAURIA.  195 

Suborder  (3).     PLEURODIRA. 

The  carapace  and  plastron  are  strongly  ossified,  and  firmly 
united  to  the  pelvis.  The  head  and  neck  can  be  folded  late- 
rally under  the  carapace,  but  cannot  be  drawn  back  under  it. 
The  cranium  has  a  more  or  less  complete  false  roof,  and  in  the 
mandibular  articulation  the  knob  is  borne  by  the  cranium,  and 
the  cup  by  the  mandible.  Chelys  is  a  well-known  genus. 

Order  4.     ICHTHYOSAURIA1. 

The  order  includes  a  number  of  large  extinct  marine 
reptiles  whose  general  shape  is  similar  to  that  of  the  Cetacea. 
The  skull  is  enormously  large,  and  the  neck  short.  The  tail 
is  very  long,  and  is  terminated  by  a  large  vertically-placed 
bilobed  fin,  the  vertebral  column  running  along  the  lower 
lobe.  The  very  numerous  vertebrae  are  short  and  deeply  bi- 
concave. The  vertebral  column  can  be  divided  into  caudal 
and  precaudal  regions  only,  as  the  ribs  which  begin  at  the 
anterior  part  of  the  neck  are  continued  to  the  posterior  end 
of  the  trunk  without  being  connected  with  any. sternum  or 
sacrum.  The  precaudal  vertebrae  bear  two  surfaces  for  the 
articulation  of  the  ribs,  while  in  the  caudal  vertebrae  the 
two  surfaces  have  coalesced.  The  caudal  region  is  also 
distinguished  by  its  chevron  bones.  The  vertebrae  have 
no  transverse  processes,  and  the  neural  arches  are  not 
firmly  united  to  the  centra,  and  have  only  traces  of  zyga- 
pophyses.  The  atlas  and  axis  are  similar  to  the  other 
vertebrae,  but  there  is  a  wedge-shaped  intercentrum  be- 
tween the  atlas  and  the  skull,  and  another  between  the 
atlas  and  the  axis.  The  skull  is  greatly  elongated  (fig.  32) 
and  pointed,  mainly  owing  to  the  length  of  the  premaxillae. 
The  orbits  are  enormous,  and  there  is  a  ring  of  bones  in  the 
sclerotic  (fig.  32,  15).  The  anterior  nares  are  very  small ;  and 

1  R.  Lydekker,  Nat.  Sci.  vol.  i.  p.  514,  1892.     Further  references  are 
there  given. 

13—2 


196 


THE  VERTEBRATE  SKELETON. 


are  placed  far  back  just  in  front  of  the  orbits.     There  is  an 
interparietal  foramen,  and  the  supratemporal  fossae  (fig.  32,  9) 


FIG.  32.     LATERAL  (BELOW)  AND  DORSAL  (ABOVE)  VIEWS  or  THE  SKULL  OF 
AN  Ichthyosaurus.     (Modified  from  Deslongchamps.) 


1.  pr  em  axilla. 

2.  maxilla. 

3.  nasal. 

4.  prefrontal1, 

5.  frontal. 

6.  postfrontal1. 

7.  anterior  nares. 

8.  orbit. 

9.  supratemporal  fossa. 

10.  interparietal  foramen. 

11.  parietal. 


12.  squamosal. 

13.  supratemporal. 

14.  quadrate  jugal. 

15.  sclerotic  ring. 

16.  postorbital. 

17.  jugal. 

18.  lachrymal. 

19.  dentary. 

20.  articular. 

21.  angular. 


are  very  large,  while  there  are  no  infratemporal  fossae.  An 
epipterygoid  occurs.  The  quadrate  is  firmly  fixed  to  the 
cranium,  and  there  is  a  large  parasphenoid.  There  are  large 
prefrontals,  but  the  frontals  are  very  small.  The  very  numer- 
ous teeth  are  large  and  conical,  and  are  placed  in  continuous 


1  The  exact  position  of  the  suture  between  the  prefrontal  and  post- 
frontal  is  not  known. 


REPTILIA.      ICHTHYOSAURIA.  197 

grooves  without  being  ankylosed  to  the  bone.  They  are 
confined  to  the  jaw-bones. 

The  ribs  are  long,  and  the  anterior  ones  have  capitula  and 
tubercula.  There  is  no  sternum,  but  the  ventral  body  wall 
is  strengthened  by  a  complex  system  of  abdominal  splint  ribs. 

The  pectoral  girdle  is  strongly  developed,  the  scapulae  are 
narrow,  the  coracoids  broad,  and  meet  ventrally  without  over- 
lapping. There  are  probably  no  precoracoids,  but  clavicles 
and  a  T-shaped  interclavicle  are  well  developed. 

The  limbs  are  very  short,  and  completely  modified  into 
swimming  paddles.  The  humerus  and  femur  are  both  short, 
while  the  radius  and  ulna,  tibia  and  fibula  are  generally  still 
further  reduced  to  the  form  of  short  polygonal  bones. 

The  digits  are  formed  of  longitudinal  series  of  very  numer- 
ous small  bones.  The  number  of  digits  is  five,  but  there 
sometimes  appear  to  be  more  owing  to  the  bifurcation  of 
certain  of  them,  or  to  the  addition  of  marginal  bones,  either 
to  the  radial  or  ulnar  side  of  the  limb.  The  humerus  has  no 
foramen,  and  both  humerus  and  femur  are  unique  in  that 
they  are  distally  terminated  by  concave  surfaces  instead  of 
by  convex  condyles.  The  pelvic  limb  is  much  smaller  than 
the  pectoral.  The  pelvis  has  no  bony  connection  with  the 
vertebral  column,  and  all  the  component  bones  are  small  and 
rod-like. 

The  Ichthyosau.ria  are  confined  to  beds  of  Secondary  age 
and  by  far  the  best  known  genus  is  Ichthyosaurus. 

Order  5.     RHYNCHOCEPHALIA. 

This  order  includes  the  living  Sphenodon  (Hatteria)  and 
various  extinct  forms.  The  general  shape  of  these  animals  is 
lizard-like  and  the  tail  is  long. 

The  vertebrae  are  amphicoelous  or  sometimes  nearly  flat, 
and  the  notochord  sometimes  persists  to  some  extent.  Protero- 
saurus  differs  from  the  other  members  of  the  order  in  having 
opisthocoelous  cervical  vertebrae. 


198  THE  VERTEBRATE  SKELETON. 

The  sacrum  is  composed  of  two  vertebrae.  Ossified  inter- 
centra  (interdorsalia)  generally  occur  in  the  cervical  and 
caudal  regions,  and  sometimes  throughout  the  whole  vertebral 
column.  In  the  skull  the  quadrate  is  immovably  fixed  and 
united  to  the  pterygoid.  The  palate  is  well  ossified,  while 
the  premaxillae  which  are  often  beak-like  are  never  ankylosed 
together.  The  jaws  may  be  toothless  or  may  be  provided 
with  teeth  which  are  usually  acrodont  (see  p.  199).  The 
palatines  frequently  bear  teeth,  and  in  Proterosaurus  teeth 
occur  also  on  the  pterygoids  and  vomers.  The  rami  of  the 
mandible  are  united  by  ligament  at  the  symphysis  except  in 
the  Rhynchosauridae,  in  which  the  union  is  bony.  Superior 
and  inferior  temporal  arcades  occur. 

The  ribs  have  capitula  and  tubercula,  and  often  uncinate 
processes  (see  p.  190)  as  in  birds.  A  pectoral  girdle  and 
sternum,  with  clavicles  and  a  T-shaped  interclavicle  are  de- 
veloped, and  abdominal  ribs  are  always  found.  The  precoracoid 
is  however  absent.  The  limbs  are  pentedactylate. 

Sphenodon1  (Hatteria)  now  living  in  some  of  the  islands 
of  the  New  Zealand  group,  is  certainly  the  most  generalised 
of  all  living  reptiles.  Though  lizard-like  in  form  it  differs 
from  all  living  lizards  in  the  possession  of  two  temporal 
arcades,  abdominal  ribs  and  a  fixed  quadrate ;  and  is  often 
considered  to  be  nearly  allied  in  many  respects  to  the  type 
of  reptile  from  which  all  the  others  took  their  origin. 

Among  the  better  known  extinct  forms  are  Proterosaurus 
of  Permian  and  Hyperodapedon  of  Triassic  age. 

Order  6.     SQUAMATA. 

This  order  includes  the  extinct  Mosasaurians,  and  the 
lizards  and  snakes  which  form  the  vast  majority  of  living 
reptiles.  The  trunk  may  be  moderately  elongated  and  provided 

1  A.  Giinther,  On  the  Anatomy  of  Hatteria,  Phil.  Trans,  vol.  157,  1867, 
p.  595. 


REPTILIA.      SQUAMATA.  199 

with  four  short  limbs  as  in  lizards,  or  it  may  be  limb- 
less, extremely  elongated,  and  passing  imperceptibly  into 
the  tail.  The  surface  is  generally  completely  covered  with 
overlapping  horny  epidermal  scales,  below  which  bony  dermal 
scutes  may  be  developed. 

The  vertebrae  are  procoelous,  rarely  amphicoelous.  There 
are  no  intercentra,  and  the  neural  arches  are  firmly  united  to 
the  centra.  Additional  articulating  surfaces,  the  zygosphenes 
and  zygantra,  are  often  developed1.  The  sacrum  is  formed 
of  two  or  rarely  three  vertebrae,  or  may  be  wanting  as  in 
Ophidia.  In  the  skull  an  infratemporal  arcade  forming  the 
lower  boundary  of  the  infratemporal  fossa  is  absent,  and  the 
quadrate,  except  in  the  Chamaeleons,  is  movably  articulated 
to  the  squamosal.  The  palatal  vacuities  are  large  and  the 
nares  are  separate.  There  is  often  a  distinct  parasphenoid. 
The  teeth  are  either  acrodont  (i.e.  ankylosed  to  the  summit 
of  the  jaw),  or  pleurodont,  i.e.  ankylosed  to  the  inner  side 
of  the  jaw.  The  thoracic  ribs  each  have  a  single  head 
which  articulates  with  the  centrum  of  the  vertebra;  while 
uncinate  processes  and  abdominal  ribs  never  occur. 

A  pectoral  girdle  and  sternum  may  be  present,  or  may  be 
completely  absent  as  in  snakes.  Except  in  snakes  there  are 
generally  four  pentedactylate  limbs  which  may  either  form 
paddles  or  be  adapted  for  walking. 

Suborder  (1).     LACERTiLiA2. 

The  body  is  elongated,  and  as  a  rule  four  short  pentedacty- 
late limbs  are  present,  but  sometimes  limbs  are  vestigial  or 

1  Zygosphenes  are  extra  articulating  surfaces  borne  upon  the  anterior 
face  of  the   neural  arch  ;    they  fit  into  corresponding   structures,  the 
zygantra,  which  are  borne  on  the  posterior  surface  of  the  neural  arch 
of  the  preceding  vertebra.     Ordinary  zygapophyses  always  accompany 
them. 

2  See  E.  D.  Cope,  P.  Amer.  Phil.  Soc.  vol.  xxx.  p.  185. 


200          THE  VERTEBRATE  SKELETON. 

absent.  The  exoskeleton  generally  has  the  form  of  horny 
plates,  spines,  or  scales ;  while  sometimes  as  in  the  Chamae- 
leons  and  Amphisbaenians  it  is  absent.  In  other  forms  such 
as  Tiliqua  and  Scincus,  the  body  has  a  complete  armour  of 
bony  scutes,  whose  shape  corresponds  with  that  of  the  over- 
lying horny  scales. 

The  vertebrae  are  precocious,  rarely  as  in  the  Geckos 
amphicoelous ;  they  are  usually  without  zygosphenes  and 
zygantra,  but  these  structures  occur  in  the  Iguanidae.  The 
sacral  vertebrae  of  living  forms  are  not  ankylosed  together, 
and  the  caudal  vertebrae  usually  have  well-developed  chevron 
bones. 

In  the  skull1  the  orbits  are  separated  from  one  another, 
only  by  an  imperfectly  developed  interorbital  septum,  the 
cranial  cavity  not  extending  forwards  between  them,  while 
the  alisphenoidal  region  is  unossified.  The  premaxillae  may 
be  paired  or  united  (Amphisbaenidae),  and  there  is  usually 
an  interparietal  foramen.  There  may  be  a  complete  supra- 
temporal2  arcade  bounding  the  lower  margin  of  the  supra- 
temporal  fossa,  or  the  supratemporal  fossa  may  be  open  below. 
The  quadratojugal  is  not  ossified,  and  the  quadrate  articulates 
with  the  exoccipital.  There  is  no  infratemporal  arcade.  There 
is  commonly  a  rod-like  epipterygoid3  (fig.  33,  14)  connecting 
the  pterygoid  and  parietal. 

Teeth  are  always  present,  and  may  be  confined  to  the 
jaws  or  may  be  developed  also  on  the  pterygoids  and  rarely 
on  the  palatines ;  they  are  either  acrodont  or  pleurodont. 
The  rami  of  the  mandible  are  suturally  united. 

A  pectoral  girdle  is  always  present,  and  generally  also  a 
sternum.  Clavicles  and  a  T-shaped  interclavicle  are  commonly 
present,  but  are  absent  in  the  Chamaeleons. 

1  See  W.  K.  Parker,  Phil.  Trans,  vol.  170,  1879,  p.  595. 

2  See  p.  281. 

:{  Often  called  the  columella  cranii. 


REFflLIA.      LACERTILIA. 

19          20 

L.J* 


201 


-S3 


FIG.  33.     A,  LATERAL  VIEW,  AND 
OF  A  LIZARD  ( Varanus 

1.  premaxilla. 

2.  maxilla. 

3.  nasal. 

4.  lateral  ethmoid. 

5.  supra-orbital. 

6.  lachrymal. 

7.  frontal. 

8.  postfrontal. 

9.  prefrontal. 

10.  basisphenoid. 

11.  pro-otic. 

12.  epi-otic. 

13.  pterygoid. 

14.  epipterygoid   (columella 

cranii). 

15.  jugal. 


B,  LONGITUDINAL  SECTION   OF   THE   SKULL 

varius).  x-f-.     (Brit.  Mus.) 

16.  transpalatine. 

17.  parasphenoid. 

18.  quadrate. 

19.  parietal. 

20.  squamosal. 

21.  supratemporal. 

22.  exoccipital. 

23.  dentary. 

24.  splenial. 

25.  supra-angular. 

26.  angular. 

27.  coronoid. 

28.  articular. 

29.  vomer. 

30.  basi-occipital. 

31.  orbitosphenoid. 


202          THE  VERTEBRATE  SKELETON. 

There  is  no  separate  precoracoid  but  a  precoracoidal  pro- 
cess (fig.  34,  7)  of  the  coracoid  is  generally  prominent. 


FIG.  34.     LATERAL  VIEW  or  THE  SHOULDER-GIRDLE  OF  Varanus.      x  f . 
(Brit.  Mus.). 

1.  suprascapula.  5.     clavicle. 

2.  scapula.  6.     interclavicle. 

3.  glenoid  cavity.  7.     precoracoidal  process. 

4.  coracoid. 

Sternal  ribs  are  present  in  chamaeleons  and  scinks.  The 
limbs  are  in  the  great  majority  of  cases  pentedactylate  and 
the  digits  are  clawed.  The  phalanges  articulate  by  means 
of  condyles.  Sometimes  one  or  both  pairs  of  limbs  are 
absent.  When  the  posterior  limbs  are  absent  the  pelvis  is 
also  wanting,  though  the  loss  of  the  anterior  limbs  does  not 
lead  to  a  corresponding  loss  of  the  pectoral  girdle. 

The  pubis  corresponds  to  the  prepubis  of  Dinosaurs,  and 
both  pubes  and  ischia  meet  in  ventral  symphyses. 

The  suborder  includes  the  Lizards,  Chamaeleons  and  Arn- 
phisbaenians. 

Suborder  (2).     OPHIDIA1. 
The  Ophidia  or  snakes  are  characterised  by  their  greatly 

1  See  C.  K.  Hoffmann,  in  Bronn's  Klassen  und  Ordnungen  des  Thier- 
reichs,  Bd.  vi.,  3  abth.  1885—90. 


REPTILIA.       OPH1DIA.  203 

elongated  body  and  want  of  limbs.  The  body  is  covered  with 
overlapping  horny  scales  and  bony  dermal  scutes  are  never 
present.  The  vertebrae  are  precocious,  and  are  distinguishable 
into  two  groups  only,  precaudal  or  rib-bearing,  and  caudal  or 
ribless.  The  atlas  vertebra  is  also  ribless.  The  neural  arches 
are  always  provided  with  zygospheiies  and  zygantra.  Many 
of  the  vertebrae  have  strong  hypapophyses,  and  the  caudal 
vertebrae  are  without  chevron  bones. 

In  the  skull  the  cranial  cavity  extends  forwards  between 
the  orbits,  and  is  closed  in  front  by  downgrowths  from  the 
f  rontals  and  parietals  which  meet  the  well-ossified  alisphenoids 
and  orbitosphenoids1.  The  cranium  is  strongly  ossified,  and 
there  are  no  parotic  processes  or  interparietal  foramen.  There 
are  no  temporal  arcades  and  no  epipterygoid.  The  premaxillae 
if  present  are  very  small  (fig.  51,  1)  and  usually  toothless. 
The  quadrates  articulate  with  the  squamosals,  and  do  not  as 
in  Lacertilia  meet  the  exoccipitals.  The  palatines  do  not 
unite  directly  with  the  vomers  or  with  the  base  of  the  cranium, 
and  the  whole  pala to-maxillary  apparatus  is  more  loosely  con- 
nected with  the  cranium  than  it  is  in  Lacertilia.  The  ptery- 
goids,  and  in  most  cases  also  the  palatines,  bear  teeth.  The 
dentition  is  acrodont,  and  the  rami  of  the  mandible  are  united 
only  by  an  elastic  ligament — an  important  point  serving  to 
distinguish  the  Ophidia  from  the  Lacertilia.  There  is  an 
imperfectly  developed  interorbital  septum,  the  ventral  part 
of  which  is  formed  by  the  paraspherioid.  The  postfrontal  is 
generally  well  developed,  while  the  jugals  and  quadratojugals 
are  absent.  There  are  never  any  traces  of  the  anterior  limbs 
or  pectoral  girdle,  but  occasionally  there  are  vestiges  of  a 
pelvis  and  posterior  limbs. 

1  Some  anatomists  consider  that  the  closing  in  of  the  brain  case  in 
front  is  entirely  due  to  the  frontals  and  parietals. 


204  THE   VERTEBRATE   SKELETON. 

Suborder  (3).     PYTHONOMORPHA'. 

This  suborder  includes  Mosasaurus  and  its  allies,  a  group 
of  enormous  extinct  marine  reptiles  found  in  beds  of  Cre- 
taceous age. 

The  skin  is  in  most  forms  at  any  rate  unprovided  with 
dermal  scutes.  The  vertebrae  may  be  with  or  without  zygo- 
sphenes  and  zygantra.  The  skull  resembles  that  of  lizards, 
having  an  interparietal  foramen,  and  a  cranial  cavity  open 
in  front.  The  squamosal  takes  part  in  the  formation  of  the 
cranial  wall,  and  the  quadrate  articulates  with  the  squamosal, 
not  as  in  Lacertilia  with  the  exoccipital.  There  are  large 
supratemporal  fossae,  bounded  below  by  supratemporal  arcades. 
The  teeth  are  large  and  acrodont,  and  occur  on  the  pterygoids 
as  well  as  on  the  jaws.  The  two  rami  of  the  mandible  are 
united  by  ligament  only.  Pectoral  and  pelvic  girdles  are 
present,  but  clavicles  are  wanting,  and  the  pelvis  is  not  as  a 
rule  united  to  any  sacrum. 

The  limbs  are  pentedactylate,  and  are  adapted  for  swim- 
ming, while  all  the  limb  bones  except  the  phalanges  are  rela- 
tively very  short.  The  number  of  phalanges  is  riot  increased 
beyond  the  normal,  and  they  articulate  with  one  another  by 
flat  surfaces.  The  terminal  phalanges  are  without  claws. 

Order  7.     DiNOSAURiA2. 

The  extinct  reptiles  comprising  this  order  were  all  terres- 
trial, and  include  the  largest  terrestrial  animals  known.  They 

1  E.  D.  Cope,  Eep.  U.  8.  Geol.  Surv.,  1875,  vol.  n.,  The  vertebrata 
of  the  Cretaceous  formations  of  the  west.     E.  D.  Cope,  P.  Boston  Soc. 
1862,  xii.  p.  250.     0.  C.  Marsh,  Amer.  J.  Sci.  1872,  vol.  3.     B.  Owen, 
Quart.  J.  Geol.  Soc.  1877,  and  1878. 

2  J.  W.  Hulke,   Presidential  address   to   the  Geol.   Soc.  of  London, 
1883  and  1884.     0.  C.  Marsh,  many  papers  in  the  Amer.  J.  Sci.  from 
1878   onwards,  also  in   the  Geol.  Mag.     E.  Owen,  History   of  British 
fossil  reptiles  :  Dinosauria  (Palaeont.  Soc.). 


REPTILIA.      DINOSAURIA.  205 

vary  greatly  in  size  and  in  the  structure  of  the  limbs,  some 
approach  close  to  the  type  of  structure  met  with  in  birds, 
others  are  allied  to  crocodiles, 

Passing  to  the  more  detailed  characters  : — there  is  some- 
times a  well-developed  exoskeleton  having  the  form  of  bony 
plates  or  spines.  The  vertebrae  may  be  solid  or  their  centra 
may  be  hollowed  internally ;  their  surfaces  may  be  flat,  bi- 
concave or  opisthocoelous.  The  sacrum  is  composed  of  from 
two  to  six  vertebrae. 

As  regards  the  skull,  the  quadrate  is  large  and  fixed,  and 
supratemporal  and  infratemporal  fossae  bounded  by  bone  occur. 
The  teeth  are  more  or  less  laterally  compressed,  and  often 
have  serrated  edges ;  they  may  be  placed  in  distinct  sockets 
or  in  a  continuous  groove.  The  ribs  have  capitula  and  tuber- 
cula,  and  sternal  ribs  often  occur.  The  scapula  is  very  large, 
the  coracoid  small,  and  there  is  no  precoracoid,  or  T-shaped 
interclavicle.  Clavicles  are  only  known  in  a  few  cases.  In 
the  pelvis  the  ilium  is  elongated  both  in  front  of,  and  behind, 
the  acetabulum,  sometimes  the  pre-pubis,  sometimes  the  post- 
pubis  is  the  better  developed.  The  anterior  limbs  are  shorter 
than  the  posterior,  and  the  long  bones  are  sometimes  solid, 
sometimes  hollow. 

There  are  three  well-marked  suborders  of  the  Dinosauria. 

Suborder  (1).     SAUROPODA1. 

The  reptiles  belonging  to  this  group  were  probably  quadru- 
pedal and  herbivorous. 

They  have  the  cervical  and  anterior  trunk  vertebrae 
opisthocoelous,  while  the  posterior  vertebrae  are  biconcave; 
all  the  presacral,  and  sometimes  the  sacral  vertebrae  are 
hollowed  internally.  The  teeth  are  spatulate  and  without 
serrated  edges,  they  are  always  planted  in  distinct  sockets, 
and  some  of  them  are  borne  by  the  premaxillae. 

1  The  diagnostic  characters  of  the  different  groups  of  Dinosaurs  are 
in  the  main  those  given  by  von  Zittel. 


206 


THE  VERTEBRATE  SKELETON. 


REPTILIA.      DINOSAURIA.  207 

1.  anterior  nares.  5.     scapula. 

2.  prominence    on    the    nasal  6.     coracoid. 

bones      which      probably  7.  ilium. 

carried  a  horn.  8.  pubis  (pre-pubis). 

3.  pre-orbital  vacuity.  9.  ischium. 

4.  orbit. 

The  nares  have  the  form  of  long  slits  and  there  are  large 
pre-orbital  vacuities. 

The  limb  bones  are  solid,  and  the  anterior  limbs  are  not 
much  shorter  than  the  posterior  ones.  All  the  limbs  are 
plantigrade  and  pentedactylate,  and  the  digits  of  the  pes  are 
clawed.  There  is  a  large  pre-pubis  directed  downwards  and 
forwards,  meeting  its  fellow  in  a  ventral  symphysis,  but  there 
is  no  post-pubis. 

The  Sauropoda  are  found  in  the  secondary  rocks  of  Europe 
and  N.  America  and  include  the  largest  land  animals  that  are 
known  to  have  existed.  Many  of  the  best  known  forms  such 
as  Brontosaurus  and  Morosaurus  are  North  American. 


Suborder  (2).     THEROPODA. 

The  members  of  this  suborder  were  all  carnivorous,  and 
from  the  small  comparative  size  of  the  anterior  limbs  many  of 
them  were  probably  bipedal. 

The  vertebrae  are  opisthocoelous  or  amphicoelous,  their 
neural  arches  are  provided  with  zygosphenes  and  zygantra, 
and  their  centra  are  frequently  hollowed  internally ;  the  limb 
bones  are  also  hollow,  and  in  fact  the  whole  skeleton  is  ex- 
tremely light.  The  tail  is  of  great  length.  The  teeth  are 
pointed  and  recurved,  and  have  one  or  both  borders  serrated ; 
they  are  always  planted  in  distinct  sockets,  and  some  of  them 
are  borne  by  the  premaxillae.  There  are  large  pre-orbital 
vacuities.  The  digits  of  both  manus  and  pes  are  terminated 
by  pointed  ungual  phalanges  which  must  have  borne  claws. 
In  the  pelvis  the  pre-pubes  and  ischia  are  slender  bones,  the 


208          THE  VERTEBRATE  SKELETON. 

former  meeting  in  a  ventral  symphysis.  The  ilia  are  very 
deep  vertically  and  there  are  no  post-pubes.  The  astragalus 
is  closely  applied  to  the  tibia,  in  front  of  which  it  sends  an 
ascending  process,  sometimes  the  two  bones  appear  to  have 
been  ankylosed  together,  as  in  birds.  The  metatarsals  are 
elongated  and  the  feet  digitigrade. 

The  Theropoda  vary  greatly  in  size,  one  of  the  best  known 
genera  Compsognathus  was  about  as  large  as  a  cat,  another, 
Megalosaurus,  perhaps  as  large  as  an  elephant.  Ceratosaurus 
is  the  name  of  a  well-known  North  American  form  regarded 
by  many  authorities  as  identical  with  Megalosaurus. 

Suborder  (3).     ORTHOPODA. 

This  suborder  includes  the  most  specialised  of  the  Dino- 
saurs, certain  of  which  resemble  the  Theropoda  in  being 
bipedal.  In  some  of  them  such  as  Stegosaurus  the  exoskeleton 
is  strongly  developed,  in  others  such  as  Iguanodon  it  is 
absent. 

The  vertebrae  are  solid  and  may  be  opisthocoelous,  bi- 
concave, or  flat.  The  teeth  are  compressed  and  serrated, 
often  irregularly,  and  are  frequently  not  set  in  distinct  sockets. 
The  anterior  part  of  the  premaxillae  is  without  teeth,  and  a 
toothless  pre-dentary  or  mento-meckelian  bone  is  present. 
The  pre-orbital  vacuities  are  small  or  absent,  and  the  nares 
are  large  and  placed  far  forwards. 

The  most  characteristic  features  of  the  group  are  found 
in  the  pelvis  which,  except  in  the  Ceratopsia,  bears  a  striking 
resemblance  to  that  of  birds.  The  ischium  and  post-pubis 
are  long  slender  bones  directed  backwards  parallel  to  one 
another,  and  the  pre-pubis  is  also  well  developed.  The  ischium 
has  an  obturator  process.  The  limb  bones  are  sometimes 
hollow,  sometimes  solid.  The  anterior  limbs  are  much  shorter 
than  the  posterior,  pointing  to  a  bipedal  method  of  progression. 
The  pes  is  digitigrade  or  plantigrade,  and  has  three,  rarely  four, 
digits. 


REPTILIA.      DINOSAURIA.  209 

The  suborder  Orthopoda  may  be  further  subdivided  into 
three  sections : — 

A.     STEGOSAURIA. 

A  dermal  exoskeleton  is  strongly  developed.  The  verte- 
bral centra  are  flat  or  biconcave,  and  neither  they  nor  the 
limb  bones  are  hollowed  out  by  internal  cavities.  The  limbs 
are  plantigrade,  the  anterior  ones  short,  the  posterior  ones 
very  large  and  strong.  The  post-pubis  is  well  developed ; 

e.g.  Stegosaurus  from  the  Upper  Jurassic  of  Colorado. 

B.  CERATOPSIA. 

There  is  sometimes  a  well-developed  dermal  exoskeleton 
formed  of  small  granules  and  plates  of  bone.  The  bones  are 
solid,  and  the  vertebral  centra  flat.  The  cranium  bears  a 
pair  of  enormous  pointed  frontal  horns,  and  the  parietal  is 
greatly  expanded  and  elevated  behind,  forming  with  the 
squamosals  a  shield  which  overhangs  the  anterior  cervical 
vertebrae.  The  premaxillae  are  united,  and  in  front  of  them 
is  a  pointed'  beak-like  bone  which  bites  upon  a  toothless 
predentary  ossification  of  the  mandible.  The  teeth  have  two 
roots.  The  anterior  limbs  are  but  little  shorter  than  the 
posterior  ones.  There  is  no  post-pubis ; 

e.g.  Polyonax  from  the  uppermost  Cretaceous  of  Montana. 

C.  ORNITHOPODA1. 

There  is  no  dermal  exoskeleton.  The  cervical  vertebrae 
are  opisthocoelous,  and  so  are  sometimes  the  thoracic.  The 
limb  bones  are  hollow  and  the  anterior  limbs  are  much  shorter 
than  the  posterior  ones.  The  feet  are  digitigrade  and  pro- 
vided with  long  pointed  claws.  The  post-pubis  is  long  and 
slender  and  directed  back  parallel  to  the  ischium ; 

e.g.  Iguanodon  from  the  European  Cretaceous. 

1  See  0.  C.  Marsh,  Amer.  J.  Set.  (3),  vol.  48,  1894,  p.  85. 
R.  14 


210  THE   VERTEBRATE    SKELETON. 

Order  8.     CnocoDiLiA1. 

This  order  includes  the  Crocodiles,  Alligators  and  Garials 
and  various  extinct  forms,  some  of  which  are  closely  allied  to 
the  early  Dinosaurs. 

There  is  always  a  more  or  less  complete  exoskeleton  formed 
of  bony  scutes  overlain  by  epidermal  scales  ;  these  bony  scutes 
are  specially  well  developed  on  the  dorsal  surface  but  may 
occur  also  on  the  ventral.  The  vertebral  column  is  divisible 
into  the  five  regions  commonly  distinguishable.  In  all  living 
forms  the  vertebrae,  with  the  exception  of  the  atlas  and  axis, 
the  two  sacrals,  and  first  caudal,  are  procoelous,  but  in  many 
extinct  forms  they  are  amphicoelous.  The  atlas  (fig.  71)  is 
remarkable,  consisting  of  four  pieces,  and  the  first  caudal  is 
biconvex. 

The  teeth  are,  in  the  adult,  planted  in  separate  deep 
sockets.  The  skull  is  very  dense  and  solid,  and  all  the 
component  bones  including  the  quadrate  are  firmly  united. 
The  dorsal  surface  of  the  skull  is  generally  characteristically 
sculptured.  There  is  an  interorbital  septum,  and  the  orbito- 
sphenoidal  and  presphenoidal  regions  are  imperfectly  ossified. 
Supratemporal,  infratemporal,  and  post-temporal  fossae  occur, 
but  no  interparietal  foramen.  In  living  genera  there  is  a  long 
secondary  palate  formed  by  the  meeting  in  the  middle  line  of 
the  palatines,  pterygoids  and  maxillae  (fig.  43,  A). 

Cervical  ribs  (fig.  41,  8  and  9)  are  well  developed,  and  arti- 
culate with  rather  prominent  surfaces  borne  on  the  neural 
arches  and  centra  respectively.  The  thoracic  ribs  articulate 
with  the  long  transverse  processes,  and  sternal  ribs  and 

1  See  C.  B.  Briihl,  Das  skelet  der  Krokodiliden,  Wien,  1862.  C.  K. 
Hoffmann  in  Bronn's  Klassen  und  Ordnungen  des  Thier-reichs,  Bd.  vi. 
Abth.  in.  1881—85.  T.  H.  Huxley,  Proc.  Linn.  Soc.  (Zoology)  1860 
vol.  iv.  p.  1.  E.  Owen,  History  of  British  fossil  Reptiles.  Crocodilia 
(Palaeont.  Soc.).  A.  Smith  Woodward,  Geol.  Mag.  1885,  3rd  dec.  H.  p. 
496.  A.  Smith  Woodward,  Proc.  of  Geologists'  Assoc.  vol.  ix.  p.  288, 1886. 


REPTILIA.      CROCODILIA.  211 

abdominal  splint  ribs  (fig.  46,  4)  occur.  The  sternum  is  carti- 
laginous, and  both  it  and  the  shoulder-girdle  are  very  simple. 
The  precoracoid  is  represented  by  merely  a  small  process  on 
the  coracoid,  while  the  clavicles  are  absent,  except  in  the 
Parasuchia.  In  the  pelvis  (fig.  49)  there  is  a  large  ilium,  and 
an  ischium  meeting  its  fellow  in  a  ventral  symphysis ;  these 
two  bones  form  almost  the  whole  of  the  acetabulum.  In 
front  of  the  acetabulum,  in  the  Eusuchia,  projects  a  bone 
which  is  generally  called  the  pubis,  but  is  in  reality  rather 
an  epipubis  (fig.  49,  4),  the  true  pubis  being  probably  repre- 
sented by  a  fourth  element  which  remains  cartilaginous  for 
some  time,  and  later  on  ossifies  and  attaches  itself  to  the 
ischium.  The  limbs  are  small  in  proportion  to  the  size  of  the 
body,  and  are  adapted  for  swimming  or  for  shuffling  along  the 
ground ;  they  are  plantigrade  and  the  bones  are  all  solid. 
In  living  forms  the  anterior  limbs  have  five  digits  and  the 
posterior  four,  the  fifth  being  represented  only  by  a  short 
metatarsal.  The  first  three  digits  in  each  case  are  clawed. 
The  calcaneum  has  a  large  back  ward  ly-projecting  process. 

The  order  Crocodilia  may  be  subdivided  into  two  sub- 
orders. 

Suborder  (1).     PARASUCHIA. 

The  vertebral  centra  are  flat  or  biconcave.  The  pre- 
maxillae  are  very  large,  and  the  nares  are  separated,  and 
placed  far  back.  The  posterior  narial  openings  lie  compara- 
tively far  forward  between  the  anterior  extremities  of  the 
palatines. 

The  palatines  and  pterygoids  do  not  form  a  secondary 
palate.  The  supratemporal  fossae  are  small,  and  open  poste- 
riorly, the  lateral  temporal  fossae  are  very  large.  The  parietals 
and  frontals  are  paired.  Clavicles  are  present.  The  best 
known  and  most  important  genus  of  these  extinct  crocodiles 
is  Belodon. 

14—2 


212  THE   VERTEBRATE   SKELETON. 

Suborder  (2).     EUSUCHIA. 

The  vertebrae  are  either  biconcave  or  procoelous.  The  pre- 
maxillae  are  small,  and  the  anterior  nares  are  united  and 
placed  far  forwards.  The  posterior  nares  lie  far  back,  the 
palatines  and  in  living  genera  the  pterygoids,  meeting  in  the 
middle  line,  and  giving  rise  to  a  closed  palate.  The  supra- 
temporal  fossae  are  surrounded  by  bone  on  all  sides,  and  the 
parietals,  and  often  also  the  frontals  are  united.  There  are 
no  clavicles.  The  suborder  includes  the  genera  Crocodilus, 
Alligator,  Garialis  and  others  living  and  extinct. 

Order  9.     PTEROSAURIA1. 

These  animals,  called  also  the  pterodactyles  or  Ornitho- 
sauria,  are  a  group  of  extinct  reptiles,  whose  structure  has 
been  greatly  modified  from  the  ordinary  reptilian  type  for  the 
purpose  of  flight. 

The  skin  was  naked  and  they  vary  greatly  in  size  and  in 
the  length  of  the  tail.  The  vertebrae  and  limb  bones  are 
pneumatic  just  as  in  birds.  The  presacral  vertebrae  are  pro- 
coelous and  have  their  neural  arches  firmly  united  to  the 
centra.  The  neck  is  long,  the  caudal  vertebrae  are  amphi- 
coelous,  and  from  three  to  five  vertebrae  are  fused  together 
in  the  sacral  region.  The  skull  is  large  and  somewhat  bird- 
like,  the  facial  portion  being  much  drawn  out  anteriorly,  and 
the  sutures  being  obliterated.  It  resembles  that  of  other 
reptiles  in  having  large  supratemporal  fossae  ;  large  pre-orbital 
vacuities  also  occur.  The  jaws  may  be  toothed  or  toothless, 
and  the  teeth,  when  present,  are  imbedded  in  separate  sockets. 
The  premaxillae  are  large,  and  the  quadrate  is  firmly  attached 
to  the  skull.  The  rami  of  the  mandible  are  united  at  the 

1  See  H.  G.  Seeley  On  the  Organisation  of  the  Ornithosauria,  Journ. 
Linn.  Soc.  (Zoology)  vol.  xin.  p.  84.  K.  A.  Zittel,  Ueber  Flugsaurier  aus 
dem  lithographischen  schiefer,  Palaeontograph.  xxix.  p.  49. 


REPTILTA.      PTEROSAURIA.  213 

symphysis,  and  there  is  an  ossified  ring  in  the  sclerotic.  The 
occurrence  of  a  postfrontal  and  its  union  with  the  jugal 
behind  the  orbit,  are  characteristic  reptilian  features. 

The  ribs  have  capitula  and  tubercula,  and  sternal  and 
abdominal  ribs  occur.  The  sternum  has  a  well-developed  keel, 
and  the  scapula  and  coracoid  are  large  and  bird-like.  There 
are  no  clavicles  or  interclavicle. 

The  anterior  limbs  are  modified  to  form  wings  by  the  great 
elongation  of  the  fifth  digit,  to  which  a  membrane  was  at- 
tached. The  second,  third  and  fourth  digits  are  clawed  and 
are  not  elongated  in  the  way  that  they  are  in  bats.  The 
pollex,  if  present  at  all,  is  quite  vestigial. 

The  pelvis  is  weak  and  small,  and  though  the  ilia  are  pro- 
duced both  in  front  of  and  behind  the  acetabula,  in  other 
features  the  pelvis  is  not  bird-like.  The  ischia  are  short  and 
wide,  and  the  pubes  are  represented  only  by  the  pre-pubes. 
The  posterior  limbs  are  small  and  the  fibula  is  much  reduced. 
The  pes  is  quite  reptilian  in  type,  and  has  five  separate  slender 
metatarsals.  The  two  best  known  genera  are  Pterodactylus,  in 
which  the  tail  is  short,  and  Rhamphorhynchus,  in  which  it  is 
long.  The  Pterosauria  are  found  throughout  the  Jurassic  and 
Cretaceous  formations  in  both  Europe  and  North  America. 


CHAPTER   XIV. 

THE  SKELETON  OF  THE  GREEN  TURTLE. 

(Chelone  midas.) 

THE  most  striking  feature  as  regards  the  skeleton  of  the 
Turtle  is  that  the  trunk  is  enveloped  in  a  bony  box,  the  dorsal 
portion  of  which  is  called  the  carapace,  while  the  ventral 
portion  is  the  plastron. 

I.     EXOSKELETON. 

a.  The  epidermal  exoskeleton  in  the  Green  Turtle  as 
in  all  other  Chelonia  except  Dermochelys,  Trionyx  and  their 
allies  is  strongly  developed,  its  most  important  part  consisting 
of  a  series  of  horny  shields  which  cover  over  the  bony  plates 
of  the  carapace  and  plastron  but  do  not  at  all  correspond  to 
them  in  size  and  arrangement. 

The  shields  covering  over  the  carapace  consist  of  three 
rows  of  larger  central  shields, — five  (vertebral)  shields  being 
included  in  the  middle  row  and  four  (costal)  in  each  lateral 
row, — and  of  a  number  of  smaller  marginal  shields. 

Of  the  marginal  shields,  that  lying  immediately  in  front  of 
the  first  vertebral  is  termed  the  nuchal,  while  the  two  suc- 
ceeding the  last  vertebral  are  called  sometimes  pygal,  some- 
times supracaudal ;  the  remainder  are  the  marginal  shields 
proper. 

The  epidermal  covering  of  the  plastron  consists  princi- 
pally of  six  pairs  of  symmetrically  arranged  shields,  called 


THE  SKELETON  OB1  THE  TURTLE.   THE  CARAPACE.   215 

respectively  the  gular,  humeral,  pectoral,  abdominal, 
femoral,  and  anal,  the  gular  being  the  most  anterior.  In 
front  of  the  gular  shields  is  an  unpaired  intergular,  and 
the  shields  of  the  plastron  are  connected  laterally  with  those 
of  the  carapace,  by  five  or  six  pairs  of  rather  irregular  infra- 
marginal  shields.  Smaller  horny  plates  occur  on  other  parts 
of  the  body,  especially  on  the  limbs  and  head. 

Two  other  sets  of  structures  belong  also  to  the  epidermal 
exoskeleton,  viz.  (a)  horny  beaks  with  denticulated  edges 
which  ensheath  both  upper  and  lower  jaws,  (b)  claws,  which 
as  a  rule  are  borne  only  by  the  first  digit  of  each  limb. 
Sometimes  in  young  individuals  the  second  digit  is  also  clawed. 

6.  The  dermal  exoskeleton  is  strongly  developed,  and 
is  combined  with  endoskeletal  structures  derived  from  the  ribs 
and  vertebrae  to  form  the  carapace. 

The  Carapace  (fig.  36)  consists  of  a  number  of  plates 
firmly  united  to  one  another  by  sutures.  They  have  a  very 
definite  arrangement  and  include  : 

(a)  the  nuchal  plate  (fig.  36,  1),   a  wide  plate  forming 
the  whole  of   the   anterior   margin    of   the   carapace.     It   is 
succeeded  by  three  series  of  plates,  eight  in  each  series,  which 
together  make  up  the  main  part  of  the  carapace.     Of  these 
the  small 

(b)  neural  plates1  (fig.  36,  A,  2)  form  the  middle  series. 
They  are  closely  united  with  the  neural  arches  of  the  under- 
lying vertebrae ; 

(c)  the  costal  plates1  (fig.  36,  A,  3)  are  broad  arched 
plates  united  to  one  another  by  long  straight  sutures.     They 
are  united  at  their  inner  extremities  with  the  neural  plates, 
but  the  boundaries  of  the  two  sets  of  plates  do  not  regularly 
correspond     Each  is  united  ventrally  with  a  rib  which  pro- 
jects beyond  it  laterally  for  some  distance ; 

1  Another  view  commonly  held  is  that  the  neural  and  costal  plates  are 
respectively  formed  by  the  expanded  neural  arches  and  ribs. 


216 


THE  VERTEBRATE  SKELETON. 


the  marginal  plates  (fig.  36,  4)  are  twenty-three  in 


FlG.    36.       A,    DORSAL   AND   B,    VENTRAL   VIEW   OF   THE    CARAPACE    OF   A 

LOGGERHEAD  TURTLE  (Thalassochelys  caretta),  (after  OWEN). 

1.  nuchal  plate.  6.     rib. 

2.  first  neural  plate.  7. 

3.  second  costal  plate.  8. 

4.  marginal  plate.  9. 

5.  pygal  plate. 


thoracic  vertebra. 
first  vertebral  shield. 
costal  shield. 


THE   SKELETON    OF   THE   TURTLE.       THE    PLASTRON.     217 

number,  eleven  lying  on  each  side,  while  an  unpaired  one  lies 
in  the  middle  line  posteriorly.  Many  of  them  are  marked  by 
slight  depressions  into  which  the  ends  of  the  ribs  fit ; 

(e)  the  pygal  plates  (fig.  36,  5)  are  two  unpaired  plates 
lying  immediately  posterior  to  the  last  neural. 

The  sculpturing  due  to  the  epidermal  shields  is  very 
obvious  on  the  carapace. 

The  plastron  (fig.  37)  consists  of  one  unpaired  ossification, 
the  entoplastron,  and  four  pairs  of  ossifications  called  re- 
spectively the  epiplastra,  hyoplastra,  hypoplastra,  and 
xiphiplastra. 

The  epiplastra  (fig.  37,  1)  are  the  most  anterior,  they  are 
expanded  and  united  to  one  another  in  the  middle  line  in 
front,  while  behind  each  tapers  to  a  point  which  lies  external 
to  a  process  projecting  forwards  from  the  hyoplastron.  They 
are  homologous  with  the  clavicles  of  other  vertebrates. 

The  entoplastron  or  episternum  (fig.  37,  2)  which  is 
homologous  with  the  interclavicle  of  other  reptiles,  is  ex- 
panded at  its  anterior  end  and  attached  to  the  symphysis 
of  the  epiplastra,  while  behind  it  tapers  to  a  point  and  ends 
freely. 

The  hyoplastra  are  large  irregular  bones  each  closely 
united  posteriorly  with  the  corresponding  hypoplastron,  and 
drawn  out  anteriorly  into  a  process  which  lies  internal  to  that 
projecting  backwards  from  the  epiplastron.  Each  gives  off  on 
its  inner  surface  a  slender  process  which  nearly  meets  its  fellow, 
while  the  anterior  half  of  the  outer  surface  is  drawn  out  into 
several  diverging  processes. 

The  hypoplastra  (fig.  37,  4)  are  flattened  bones  re- 
sembling the  hyoplastra,  with  which  they  are  united  by  long 
sutures ;  the  posterior  half  of  both  outer  and  inner  surfaces 
is  drawn  out  into  a  number  of  pointed  processes. 

The  xiphiplastra  are  small  flattened  elongated  bones 
meeting  one  another  in  the  middle  line  posteriorly.  In  front 
they  are  notched  and  each  interlocks  with  a  process  from  the 


218          THE  VERTEBRATE  SKELETON. 

hypoplastron  of   its  side.      The  hyoplastra,    hypoplastra  and 


FIG.  37.     THE  PLASTRON  OF  A  GREEN  TURTLE  (Chelone  midas). 
xf.     (Camb.  Mus.) 

1.  epiplastron  (clavicle).  4.     hypoplastron. 

2.  entoplastron  (interclavicle).  5.     xiphiplastron. 

3.  hyoplastron. 

xiphiplastra    are    homologous    with    the    abdominal    ribs    of 
Crocodiles. 

II.     ENDOSKELETOK 
1.     THE  AXIAL  SKELETON. 

The  axial  skeleton  includes  the  vertebral  column,  the  ribs, 
and  the  skull. 


THE  SKELETON  OF  THE  TURTLE.   THE  VERTEBRAE.  219 

A.     THE  VERTEBRAL  COLUMN  AND  RIBS. 

The  number  of  vertebrae  in  the  Green  Turtle  is  thirty- 
eight,  not  a  great  number  as  compared  with  that  in  many 
reptiles,  and  of  these  eighteen  are  caudal. 

The  vertebral  column  is  divisible  into  four  regions  only — 
cervical,  thoracic,  sacral,  and  caudal. 

THE  CERVICAL  VERTEBRAE. 

These  are  eight  in  number,  and  are  chiefly  remarkable  for 
the  great  variety  of  articulating  surfaces  which  their  centra 
present,  and  for  their  mobility  upon  one  another. 

The  first  or  atlas  vertebra  differs  much  from  all  the  others 
and  consists  of  the  following  parts  : — 

a.  the  neural  arch,  formed  of  two  separate  ossifications 
united  in  the  mid-dorsal  line ; 

b.  the  inferior  arch ; 

c.  the  centrum,  which  is  detached  from   the  rest  and 
forms  the  odontoid  process  of  the  second  vertebra. 

Each  half  of  the  neural  arch  consists  of  a  ventral  portion, 
the  pedicel,  which  lies  more  or  less  vertically  and  is  united 
ventrally  to  the  inferior  arch,  and  of  a  dorsal  portion,  the 
lamina,  which  lies  more  or  less  horizontally  and  meets  its 
fellow  in  the  middle  line  in  front,  partially  roofing  over  the 
neural  canal.  Each  pedicel  bears  a  facet  on  its  anterior 
surface,  which,  with  a  corresponding  one  on  the  inferior  arch, 
articulates  with  the  occipital  condyle  of  the  skull.  Three 
similar  facets  occur  also  on  the  posterior  surface  of  the 
pedicel  and  inferior  arch,  and  articulate  with  the  odontoid 
process.  The  laminae  meet  one  another  in  front,  but  do  not 
fuse,  while  behind  they  are  separated  by  a  wide  triangular 
space.  They  bear  a  pair  of  small  downwardly-directed  facets, 
the  postzygapophyses,  for  articulation  with  the  prezyga- 
pophyses  of  the  second  vertebra. 


220          THE  VERTEBRATE  SKELETON. 

The  inferior  arch  is  a  short  irregular  bone  bearing  two 
converging  facets  for  articulation  with  the  occipital  condyle 
and  odontoid  process  respectively. 

The  centrum  or  odontoid  process  has  a  convex  anterior 
surface  for  articulation  with  the  neural  and  inferior  arches, 
and  a  concave  posterior  surface  by  which  it  is  united  with 
the  centrum  of  the  second  or  axis  vertebra.  It  bears  pos- 
teriorly a  small  epiphysis  which  is  really  a  detached  portion  of 
the  inferior  arch. 

The  second  or  axis  and  following  five  cervical  vertebrae, 
though  showing  distinct  differences,  resemble  one  another  con- 
siderably, each  having  a  fairly  elongated  centrum  with  a  keel- 
like  hypapophysis,  each  having  also  a  neural  arch  with 
prominent  articulating  surfaces,  the  anterior  of  which,  or 
prezygapophyses,  look  upwards  and  inwards,  while  the 
posterior  ones,  the  postzygapophyses,  look  downwards  and 
outwards.  They  however,  as  was  previously  mentioned,  differ 
very  remarkably  in  the  character  of  the  articulating  surfaces 
of  the  centra.  Thus  the  second  and  third  vertebrae  are 
convex  in  front  and  concave  behind,  the  fourth  is  biconvex, 
the  fifth  is  concave  in  front  and  convex  behind.  The  sixth 
is  concave  in  front  and  attached  to  the  seventh  by  a  flat 
surface  behind,  the  seventh  has  a  flat  anterior  face  and  two 
slightly  convex  facets  behind.  The  vertebrae  all  have  short 
blunt  transverse  processes  and  the  second  has  a  prominent 
neural  spine. 

The  eighth  cervical  vertebra  is  curiously  modified,  the 
centrum  is  very  short,  has  a  rather  prominent  hypapophysis, 
and  is  convex  behind,  while  in  front  it  articulates  with  the 
preceding  centrum  by  two  concave  surfaces.  The  neural  arch 
is  deeply  notched  in  front  and  bears  two  upwardly-directed 
prezygapophyses,  while  behind  it  is  very  massive  and  is  drawn 
out  far  beyond  the  centrum,  bearing  a  pair  of  flat  postzyga- 
pophyses. The  top  of  the  neural  arch  almost  or  quite  meets 
a  blunt  outgrowth  from  the  nuchal  plate. 


THE    SKELETON    OF   THE   TURTLE.      THE   VERTEBRAE.    221 

THE  THORACIC  VERTEBRAE. 

These  are  ten  in  number  and  are  all  firmly  united  with 
the  ribs  and  elements  forming  the  carapace. 

The  first  thoracic  vertebra  differs  from  the  others,  the 
centrum  is  short  and  has  a  concave  anterior  surface  articu- 
lating with  the  centrum  of  the  last  cervical  vertebra,  and  a 
pair  of  prezygapophyses  borne  on  long  outgrowths.  The 
neural  spine  arises  only  from  the  anterior  half  of  the  centrum, 
and  is  not  fused  to  the  carapace.  Arising  laterally  from  the 
anterior  part  of  the  centrum  are  a  small  pair  of  ribs  each  of 
which  is  connected  with  a  process  arising  from  the  rib  of  the 
succeeding  vertebra. 

The  next  seven  thoracic  vertebrae  are  all  very  similar, 
each  has  a  long  cylindrical  centrum,  expanded  at  the  ends, 
and  firmly  united  to  the  preceding  and  succeeding  vertebrae. 
The  neural  arches  are  flattened  and  expanded  dorsally,  and 
are  united  to  one  another  and  to  the  overlying  neural 
plates ;  each  arises  only  from  the  anterior  half  of  its  respective 
centrum,  and  overlaps  the  centrum  of  the  vertebra  in  front  of 
it.  Between  the  base  of  the  neural  arch  and  its  successor  is  a 
small  foramen  for  the  exit  of  the  spinal  nerve.  There  are  no 
transverse  processes  or  zygapophyses. 

To  each  thoracic  vertebra  from  the  second  to  ninth  in- 
clusive, there  corresponds  a  pair  of  ribs  (fig.  36,  6)  of  a  rather 
special  character.  Each  is  suturally  united  with  the  anterior 
half  of  the  edge  of  its  own  vertebra,  and  overlaps  on  to  the 
posterior  half  of  the  edge  of  the  next  preceding  vertebra. 
The  ribs  are  much  flattened,  and  each  is  fused  with  the  cor- 
responding costal  plate,  beyond  which  it  projects  to  fit  into 
a  pit  in  one  of  the  marginal  plates. 

The  tenth  thoracic  vertebra  is  smaller  than  the  others,  and 
its  neural  arch  does  not  overlap  the  preceding  vertebra,  it 
bears  a  pair  of  small  ribs  which  are  without  costal  plates,  but 
meet  those  of  the  ninth  vertebra. 

There  are  no  lumbar  vertebrae. 


222          THE  VERTEBRATE  SKELETON. 

THE  SACRAL  VERTEBRAE. 

The  sacral  vertebrae  are  two  in  number,  they  are  short 
and  wide,  their  centra  are  ankylosed  together,  and  their  neural 
arches  are  not  united  to  the  carapace. 

The  first  has  the  anterior  face  of  the  centrum  concave  and 
the  posterior  flat,  while  both  faces  of  the  second  are  flat. 
Each  bears  a  pair  of  short  ribs  which  meet  the  ilia,  but  are 
not  completely  ankylosed  either  with  them  or  the  centra. 

THE  CAUDAL  VERTEBRAE. 

The  caudal  vertebrae  are  eighteen  in  number.  The 
centrum  of  the  first  is  flat  in  front  and  is  ankylosed  to 
the  second  sacral;  behind  it  is  convex.  The  others  are  all 
very  similar  to  one  another,  and  decrease  gradually  in  size 
when  followed  back.  Each  has  a  moderately  long  centrum, 
concave  in  front  and  convex  behind,  both  terminations  being 
formed  by  epiphyses.  The  neural  arch  arises  only  from  the 
anterior  half  of  the  vertebra ;  it  bears  a  blunt  truncated 
neural  spine  and  prominent  pre-  and  post-zygapophyses.  The 
first  seven  caudal  vertebrae  bear  short  ribs  attached  to  their 
lateral  margins,  the  similar  outgrowths  on  the  succeeding  ver- 
tebrae do  not  ossify  from  distinct  centres,  and  are  transverse 
processes  rather  than  ribs. 

B.     THE  SKULL. 

The  skull  of  the  Turtle  is  divisible  into  the  following  three 
parts  : — 

(1)  the  cranium ; 

(2)  the  lower  jaw  or  mandible ; 

(3)  the  hyoid. 

(1)     THE  CRANIUM. 

The  cranium  is  a  very  compact  bony  box,  containing  a 
cavity  in  which  the  brain  lies,  and  which  is  a  direct  continua- 
tion of  the  neural  canal  of  the  vertebrae. 


THE  SKELETON  OF  THE  TURTLE.   THE  SKULL.   223 

.1 


—17 


FIG.  38.     THE  SKULL  OF  THE  GREEN  TURTLE  (Chelone  midas).      x  £. 

A,    POSTERIOR    HALF,    B,    ANTERIOR  HALF.       (Brit.    MuS.) 

1.  parietal.  13.  angular. 

2.  squamosal.  14.  supra-angular. 

3.  quadrate.  15.  premaxilla. 

4.  basisphenoid.  16.  maxilla. 

5.  basi-occipital.  17.  jugal. 

6.  quadratojugal.  18.  postfrontal. 

7.  opisthotic.  19.  vomer. 

8.  exoccipital.  20.  prefrontal. 

9.  foramen  magnum.  21.  frontal. 

10.  splenial.  22.  external     auditory     meatus 

11.  articular.  leading     into      tympanic 

12.  dentary.  cavity. 


224          THE  VERTEBRATE  SKELETON. 

Like  those  of  the  skull  as  a  whole  its  component  bones  may 
be  subdivided  into  three  sets  :— 

1 .  those  forming  the  brain-case  or  cranium  proper  ; 

2.  those  developed  in  connection  with  the  special  sense 
organs ; 

3.  those  forming  the  upper  jaw  and  suspensorial  appa- 
ratus. 

Both  cartilage  and  membrane  bones  take  part  in  the  forma- 
tion of  the  skull,  and  a  considerable  amount  of  cartilage 
remains  unossified,  especially  in  the  ethmoidal  and  sphenoidal 
regions. 

1.     The  CRANIUM  PROPER  OR  BRAIN-CASE. 

The  cartilage  and  membrane  bones  of  the  brain-case  when 
taken  together  can  be  seen  to  be  more  or  less  arranged  in 
three  rings  or  segments,  called  respectively  the  occipital, 
parietal,  and  frontal  segments. 

The  occipital  segment  is  the  most  posterior  of  these,  and 
consists  of  four  cartilage  bones,  the  basi-occipital,  the  two 
exoccipitals  and  the  supra-occipital;  these  bound  the 
foramen  magnum. 

The  basi-occipital  (figs.  38  and  39,  5)  lies  ventral  to  the 
foramen  magnum  and  only  bounds  a  very  small  part  of  it ;  it 
forms  one-third  of  the  occipital  condyle  by  which  the  skull 
articulates  with  the  atlas  vertebra.  It  unites  dorsally  with 
the  exoccipitals  and  anteriorly  with  the  basisphenoid. 

The  exoccipitals  are  rather  small  bones,  which  form  the 
sides  and  the  greater  part  of  the  floor  of  the  foramen  magnum, 
and  two:thirds  of  the  occipital  condyle.  Laterally  each  is 
united  with  the  pterygoid  and  opisthotic  of  its  side.  At  the 
sides  of  the  occipital  condyle  each  exoccipital  is  pierced  by 
a  pair  of  foramina,  the  more  dorsal  and  posterior  of  which 
transmits  the  hypoglossal  nerve. 

The  supra-occipital  (fig.  39,  14)  is  a  larger  bone  than  the 
others  of  the  occipital  segment.  It  forms  the  upper  border 


THE  SKELETON  OF  THE  TURTLE.   THE  CRANIUM.   225 

of  the  foramen  magnum  and  is  drawn  out  dorsally  into  a  large 
crest  which  extends  back  far  beyond  the  occipital  condyle. 
In  the  adult  the  supra-occipital  is  completely  ankylosed  with 
the  epi-otics. 

The  Parietal  segment. 

The  ventral  portion  of  the  parietal  segment  is  formed  by 
the  basisphenoid  (figs.  38  and  39,  4)  which  lies  immediately 
in  front  of  the  basi-occipital.  A  triangular  portion  of  it  is 
seen  in  a  ventral  view  of  the  skull,  but  it  is  quickly  over- 
lapped by  the  pterygoids.  It  gives  off  dorsally  a  pair  of 
short  processes  which  meet  the  pro-otics. 

The  alisphenoidal  region  is  unossified  and  the  only  other 
constituents  of  the  parietal  segment  are  the  parietals  (fig.  39,  1). 
These  are  large  bones  which,  after  roofing  over  the  cranial 
cavity,  extend  upwards  and  become  expanded  into  a  pair  of 
broad  plates  which  unite  with  the  squamosal  and  bones  of  the 
frontal  segment  to  form  a  wide,  solid,  false  roof  to  the  skull. 
Each  also  sends  ventralwards  a  plate  which  meets  an  up- 
growth from  the  pterygoid  and  acts  as  an  alisphenoid. 

The  Frontal  segment. 

Of  the  frontal  segment  the  basal  or  presphenoidal  and 
lateral  or  orbitosphenoidal  portions  do  not  become  ossified, 
the  dorsal  portion  however  includes  three  pairs  of  membrane 
bones,  the  frontals,  prefrontals  and  post/rentals. 

Thefrontals  are  a  pair  of  small  bones  lying  immediately  in 
front  of  the  parietals,  and  in  front  of  them  are  the  prefrontals 
(tigs.  38  and  39,  20),  a  pair  of  similar  but  still  smaller  bones, 
which  are  produced  ventrally  to  meet  the  vomer  and  palatines. 
They  form  also  the  dorsal  boundary  of  the  anterior  nares. 
The  post/rentals  (figs.  38  and  39,  18)  are  larger  bones,  united 
dorsally  to  the  frontals  and  parietals,  posteriorly  to  the  squa- 
mosals,  and  ventrally  to  the  jugals  and  quadra tojugals.  All 
three  pairs  of  frontal  bones,  especially  the  postfrontals,  take 
part  in  the  bounding  of  the  orbits. 

R.  15 


226 


THE  VERTEBKATE  SKELETON. 


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THE  SKELETON  OF  THE  TURTLE.   SENSE  CAPSULES.  227 

2.     THE  SENSE  CAPSULES. 

Skeletal  structures  occur  in  connection  with  each  of  the 
three  special  sense  organs  of  hearing,  sight,  and  smell. 

The  Auditory  capsules. 

The  auditory  or  periotic  capsule  of  the  turtle  is  rather 
large  and  its  walls  are  well  ossified,  epi-otic,  pro-otic  and 
opisthotic  bones  being  present. 

The  epi-otic  (fig.  39,  13)  is  the  more  dorsal  of  the  three 
bones,  and  in  the  adult  is  completely  ankylosed  with  the  supra- 
occipital. 

The  opisthotic  (fig.  39,  8)  is  the  ventral  posterior  element. 
On  its  inner  side  it  is  united  to  the  supra-occipital  above, 
and  to  the  exoccipital  below ;  it  sometimes  becomes  com- 
pletely fused  with  the  exoccipital.  In  front  it  meets  the 
pro-otic,  and  on  its  outer  side  the  squamosal  and  quadrate. 
Its  anterior  portion  is  hollowed  out  by  the  cavity  in  which 
the  auditory  organ  lies,  it  gives  off  also  a  process  which  is 
separated  from  the  exoccipital  by  an  oval  foramen  through 
which  the  glossopharyngeal,  pneumogastric,  and  spinal  acces- 
sory nerves  leave  the  cranial  cavity. 

The  pro-otic  is  the  anterior  element;  it  meets  the  supra- 
occipital  and  opisthotic  posteriorly,  while  anteriorly  it  is 
separated  from  the  alisphenoidal  plate  of  the  parietal  and 
pterygoid  by  a  large  oval  foramen  through  which  the  maxillary 
and  mandibular  branches  of  the  trigeminal  nerve  pass  out 
(fig.  39,  V  1  &  2).  It  is  hollowed  out  posteriorly  by  the  cavity 
which  the  auditory  organ  lies,  and  its  inner  wall  as  seen  in 
longitudinal  section  is  pierced  by  a  foramen  through  which  the 
external  carotid  artery  and  facial  nerve  leave  the  cranial  cavity, 
— the  nerve  finally  leaving  the  skull  through  a  small  oval 
foramen  on  the  anterior  face  of  the  pro-otic  near  its  junction 
with  the  quadrate. 

Between  the  pro-otic  and  opisthotic  as  seen  in  a  longi- 
tudinal section  of  the  skull  is  a  large  opening  constricted  in  the 

15—2 


228          THE  VERTEBRATE  SKELETON. 

middle.  This  is  the  internal  auditory  meatus  (fig.  39, VIII.). 
Through  it  the  auditory  nerve  leaves  the  cranial  cavity  and 
enters  the  ear.  The  ramus  vestibularis  leaves  through  the  dorsal 
part  of  the  hole,  the  ramus  cochlearis  through  the  ventral. 

The  cavity  of  the  auditory  or  periotic  capsule  communi- 
cates with  the  exterior  by  a  fairly  large  hole,  the  fenestra 
ovalis,  which  lies  between  the  opisthotic  and  pro-otic,  and 
opens  into  a  deep  depression,  the  tympanic  cavity,  which 
is  seen  in  a  posterior  view  of  the  skull  lying  just  external  to 
the  exoccipital.  The  cavity  communicates  with  the  exterior  by 
a  large  opening,  the  external  auditory  meatus  (fig.  38,  22). 

Several  other  openings  are  seen  in  the  tympanic  cavity; 
through  one  at  the  extreme  posterior  end  the  pneumogastric 
and  spinal  accessory  nerves  leave  the  skull,  and  through 
another,  a  little  further  forwards,  the  glossopharyngeal. 

The  auditory  ossicles  consist  of  a  long  bony  columella, 
whose  inner  end  fits  into  the  fenestra  ovalis,  while  the  outer 
end  is  attached  to  a  small  cartilaginous  plate,  the  extra- 
eolumella,  which  is  united  to  the  tympanum. 

The  Optic  capsules. 

The  skeletal  structures  developed  in  connection  with  the 
optic  capsule  do  not  become  united  to  the  skull.  They  con- 
sist of : — 

(a)  the  sclerotic,  a  cartilaginous  sheath  investing  the  eye 
and  bearing 

(6)    a  ring  of  ten  small  bony  scales. 

There  is  no  lachrymal  bone. 

The  Olfactory  or  Nasal  capsules. 

The  basicranial  axis  in  front  of  the  basisphenoid  remains 
cartilaginous,  neither  presphenoid  nor  mesethmoid  bones  are 
developed,  and  the  orbits  in  a  dry  skull  communicate  by  a 
wide  space  through  which  the  second,  third,  fourth,  and  sixth 
cranial  nerves  pass  out.  Separate  nasal  bones  also  do  not 
occur,  the  large  prefrontals  extending  over  the  area  usually 
occupied  by  both  nasals  and  lachrymals. 


THE  SKELETON  OF  THE  TURTLE.   THE  UPPER  JAW.  229 

The  only  bone  developed  in  connection  with  the  nasal 
capsules  is  the  vomer  (fig.  39,  19),  an  unpaired  bone  lying 
ventral  to  the  mesethmoid  cartilage,  and  in  contact  laterally 
with  the  maxillae,  premaxillae  and  palatines. 

3.     THE  UPPER  JAW  AND  SUSPENSORIAL  APPARATUS. 

A  number  of  pairs  of  bones  are  developed  in  connection 
with  the  upper  jaw  and  suspensorial  apparatus,  one  pair,  the 
quadrates,  being  cartilage  bones,  while  the  rest  are  all  mem- 
brane bones. 

The  squamosals  (fig.  38,  2)  are  large  bones  which,  lying 
external  to  the  auditory  bones,  extend  dorsal  wards  to  meet 
the  parietals  and  postfrontals,  and  form  a  large  part  of  the 
false  roof  of  the  skull.  They  are  united  ventrally  with  the 
quadrates  and  quadratojugals. 

Each  quadrate  (fig.  38,  3)  forms  the  outer  boundary  of 
the  tympanic  cavity,  and  is  firmly  united  on  its  inner  side  with 
the  opisthotic,  exoccipital,  and  pterygoid.  Dorsally  it  is  fixed 
to  the  squamosal  and  anteriorly  to  the  quadratojugal.  Its 
outer  surface  is  marked  by  a  deep  recess,  and  it  ends  below 
in  a  strong  condyle  with  which  the  mandible  articulates.  In 
front  of  the  quadrates  are  a  pair  of  thin  plate-like  bones,  the 
quadratojugals  which  are  united  in  front  to  the  jugals  or  malars. 

The  jugals  (tig.  38,  17)  are  also  thin  plate-like  bones,  and 
form  part  of  the  posterior  boundary  of  the  orbit.  They  are 
attached  dorsally  to  the  postfrontals,  and  anteriorly  to  the 
maxillae,  while  each  also  sends  inwards  a  horizontal  process 
which  meets  the  pterygoid  and  palatine. 

The  maxillae  (figs.  38  and  39,  16)  are  a  pair  of  large  ver- 
tically-placed bones,  each  drawn  out  ventrally  into  a  straight, 
sharp,  cutting  edge.  They  form  the  lateral  boundaries  of  the 
anterior  nares,  and  each  sends  dorsalwards  a  process  which 
meets  the  post-frontal.  Each  also  sends  inwards  a  horizontal 
palatine  process,  which  meets  the  palatine  and  vomer,  and 
also  forms  much  of  the  floor  of  the  narial  passage. 


230          THE  VERTEBRATE  SKELETON. 

The  premaxillae  (figs.  38  and  39,  15)  are  a  pair  of  very 
small  bones  forming  the  floor  of  the  anterior  narial  opening, 
they  are  wedged  in  between  the  two  maxillae,  and  send  back 
processes  which  meet  the  vomer  and  palatines. 

The  palatines  (fig.  39,  10)  are  a  pair  of  small  bones  firmly 
united  with  the  pterygoids  behind,  with  the  maxillae  and  jugals 
externally,  and  with  the  vomer  in  the  middle  line.  Each  also 
gives  off  a  palatine  plate  which  unites  with  the  expanded  lower 
edge  of  the  vomer,  and  forms  the  ventral  boundary  of  the  pos- 
terior nares.  Anteriorly  the  palatines  form  the  posterior  bound- 
ary of  a  large  foramen  through  which  the  ophthalmic  branches 
of  the  fifth  and  seventh  nerves  pass  to  the  olfactory  organs. 

The  pterygoids  (fig.  39,  9)  are  a  pair  of  large  bones  which 
unite  with  one  another  by  a  long  median  suture.  They  are 
united  also  with  the  palatines  in  front,  and  with  the  quadrate, 
basisphenoid,  basi-occipital,  and  exoccipitals  behind.  Each 
also  sends  dorsal  wards  a  short  alisphenoid  plate  which 
meets  that  from  the  parietal. 

Piercing  the  posterior  end  of  the  pterygoid  is  the  prominent 
opening  of  the  carotid  canal;  a  bristle  passed  into  this  hole 
emerges  through  a  foramen  lying  between  the  pro-otic  and  the 
alisphenoid  process  of  the  pterygoid. 

(2)     THE  LOWER  JAW  OR  MANDIBLE. 

The  mandible  consists  of  one  unpaired  bone,  formed  by 
the  fusion  of  the  two  dentaries,  and  five  pairs  of  bones,  called 
respectively  the  articular,  angular,  supra-angular,  splenial 
and  coronoid. 

The  fused  dentaries  (fig.  38,  12)  form  by  far  the  largest  of 
the  bones  ;  they  constitute  the  flattened  anterior  part  of  the 
mandible,  and  extend  back  below  the  other  bones  almost  to 
the  end  of  the  jaw. 

The  coronoid  is  the  most  anterior  of  the  paired  bones,  it 
forms  a  prominent  process  to  which  the  muscles  for  closing 
the  jaw  are  attached. 


THE  SKELETON  OF  THE  TURTLE.   THE  HYOID.   231 

The  articular  (fig.  38,  1 1)  is  expanded,  and  with  the  supra- 
angular  forms  the  concave  articulating  surface  for  the  quadrate. 

The  splenial  (fig.  38,  10)  is  a  thin  plate  applied  to  the  inner 
surface  of  the  posterior  part  of  the  mandible. 

The  angular  (fig.  38,  13)  is  a  slender  plate  of  bone  lying 
below  the  supra-angular  and  splenial. 

(3)     THE  HYOID. 

The  hyoid  apparatus  is  well  developed,  parts  of  the  first  two 
branchial  arches  being  found,  as  well  as  of  the  hyoid  proper. 
It  consists  of  a  more  or  less  oblong  flattened  basilingual 
plate  or  body  of  the  hyoid  which  represents  the  fused 
ventral  ends  of  the  hyoid  and  branchial  arches  of  the  embryo, 
and  is  drawn  out  into  a  point  anteriorly.  The  greater  part  is 
formed  of  unossified  cartilage,  but  at  the  posterior  end  it  is 
bilobed,  and  a  pair  of  ossified  tracts  occur.  To  its  sides  are 
attached  three  pairs  of  structures,  which  are  portions  of  the 
hyoid  and  first  and  second  branchial  arches  respectively. 

The  free  part  of  the  hyoid  consists  of  a  small  piece  of 
cartilage  attached  to  the  anterior  part  of  the  basilingual  plate 
at  its  widest  portion  (fig.  53,  2). 

The  anterior  cornu  or  free  part  of  the  first  branchial 
arch  is  much  the  largest  of  the  three  structures.  Its  proximal 
portion  adjoining  the  basilingual  plate  is  cartilaginous,  as  is 
its  distal  end  ;  the  main  part  is  however  ossified. 

The  posterior  cornu  or  free  part  of  the  second  branchial 
arch  (fig.  53,  4)  consists  of  a  short  flattened  cartilaginous  bar 
arising  from  the  bilobed  posterior  end  of  the  basilingual  plate. 

The  hyoid  apparatus  has  no  skeletal  connection  with  the 
rest  of  the  skull. 

2.     THE  APPENDICULAR  SKELETON. 

This  includes  the  skeleton  of  the  two  pairs  of  limbs  and 
their  girdles. 

THE  PECTORAL  GIRDLE. 

The    pectoral    girdle    has  an    anomalous    position,    being 


232          THE  VERTEBRATE  SKELETON. 

situated  internal  or  ventral  to  the  ribs.  It  consists  of  three 
bones,  a  dorsal  bone,  the  scapula,  an  anterior  ventral  bone, 
the  precoracoid,  and  a  posterior  ventral  bone,  the  coracoid. 

The  scapula  is  a  small  somewhat  rod-shaped  bone  form- 
ing about  two-thirds  of  the  glenoid  cavity.  At  its  proximal 
end  it  is  closely  united  with  the  precoracoid,  the  two  bones 
ossifying  continuously.  It  tapers  away  distally,  and  is  directed 
dorsalwards  towards  the  carapace. 

The  precoracoid  forms  an  angle  of  about  130°  with  the 
scapula,  with  which  it  is  completely  fused  at  its  proximal  end. 
Its  distal  end  is  somewhat  expanded  and  flattened,  and  is 
terminated  by  a  fibrocartilaginous  epiprecoracoid  which 
meets  its  fellow.  It  takes  no  part  in  the  formation  of  the 
glenoid  cavity. 

The  coracoid  is  a  large  flattened  blade-shaped  bone  form- 
ing about  one-third  of  the  glenoid  cavity.  It  does  not  meet 
its  fellow  in  a  ventral  symphysis,  and  is  terminated  by  a  carti- 
laginous epicoracoid.  The  glenoid  articulating  surfaces  of 
both  scapula  and  coracoid  are  lined  by  a  thick  pad  of  car- 
tilage. 

THE  ANTERIOR  LIMB. 

This  is  divisible  into  three  portions,  the  upper  arm,  fore- 
arm and  manus. 

The  upper  arm  contains  a  single  bone,  the  humerus. 

The  humerus  (fig.  40,  A,  1)  is  a  stout,  nearly  straight,  some- 
what flattened  bone  widely  expanded  at  both  ends.  At  the 
proximal  end  is  the  large  hemispherical  head,  which  articulates 
with  the  glenoid  cavity.  Behind  the  head  the  bone  is  drawn 
out  into  another  large  rounded  process.  Below  the  head  the 
shaft  bears  a  small  outgrowth  which  is  continuous  with  a 
larger  one  on  the  flexor  surface  (see  p.  29).  The  bone  is 
terminated  distally  by  the  trochlea,  consisting  of  three 
partially  distinct  convex  surfaces  which  articulate  with  the 
bones  of  the  fore-arm. 


THE    SKELETON    OF   THE   TURTLE.      ANTERIOR   LIMB.     233 

The  fore- arm  includes  two  bones,  the  radius  and  ulna; 
both  these  are  small  bones,  and  are  immovably  fixed  to  one 
another  proximally  and  distally. 

The  radius  or  pre-axial  bone  is  the  larger  of  the  two,  and 
is  a  rod-like  bone  terminated  at  either  end  by  an  epiphysis. 
It  articulates  at  its  proximal  end  with  the  humerus,  and  at 
its  distal  end  with  the  radiale  or  scaphoid  bone  of  the  carpus. 

The  ulna  (fig.  40,  A,  3)  or  post-axial  bone  is  shorter  than 
the  radius,  and  more  expanded  at  its  proximal  end,  where  it 
articulates  with  the  humerus.  It  articulates  distally  with  the 
intermedium  (lunar)  and  the  ulnare  (cuneiform)  bones  of  the 
carpus.  All  three  bones  of  the  arm  have  their  terminations 
formed  by  epiphyses  which  ossify  from  centres  distinct  from 
those  forming  the  shafts. 

The  Manus  consists  of  the  carpus  or  wrist  and  the  hand 
which  includes  the  metacarpals  and  phalanges. 

The  carpus  consists  of  a  series  of  ten  small  bones,  one  of 
which,  the  pisiform  (fig.  40,  A,  10),  differs  from  the  others  in 
being  merely  an  ossification  in  the  tendon  of  a  muscle.  The 
remaining  nine  bones  are  arranged  in  a  proximal  row  of  three, 
the  ulnare  (fig.  40,  A,  6),  intermedium,  and  radiale,  and  a 
distal  row  of  five  (carpalia  1 — 5),  each  of  which  supports  one 
of  the  metacarpals.  A  ninth  bone,  the  centrale  (fig.  40,  A,  7), 
is  wedged  in  between  the  two  rows.  The  ulnare,  intermedium 
and  pisiform  are  comparatively  large  flattened  bones,  the  others 
are  small  and  cubical. 

The  hand.  This  is  composed  of  five  digits,  each  of  which 
consists  of  a  metacarpal  and  of  a  varying  number  of  phalanges. 

The  metacarpals.  The  first  metacarpal  (fig.  40,  A,  11) 
is  a  short  flattened  bone,  the  others  are  all  elongated  and 
cylindrical,  and  are  terminated  proximally  by  slightly  concave 
surfaces,  and  distally  by  slightly  convex  ones. 

The  phalanges.  The  first  and  fifth  digits  both  have  two 
phalanges,  the  second,  third,  and  fourth  have  each  three.  The 
distal  phalanx  of  the  first  digit  is  stout  and  curved,  and  bears 


234 


THE  VERTEBRATE  SKELETON. 


—-12 


FIG.  40.  A.  ANTERIOR  LIMB 
imbricata)  x  £  (Brit.  Mus.) 
TURTLE  (Chelone  midas)  x  \ 

1.  humerus. 

2.  radius  (almost  hidden  by 

ulna). 

3.  ulna. 

4.  radiale. 

5.  intermedium. 

6.  ulnare. 

7.  centrale. 

8.  carpale  I. 

9.  carpale  IV. 

10.  pisiform. 

11.  first  metacarpal. 


OF  A  YOUNG  HAWKSBILL  TURTLE  (Chelone 
.  B.  POSTERIOR  LIMB  OF  A  LARGE  GREEN 
j-  (Camb.  Mus.). 

12.     femur, 
the         13.     tibia. 

14.  fibula. 

15.  tibiale  intermedium  and  cen- 

trale fused. 

16.  fibulare. 

17.  tarsale  1. 

18.  tarsale  2. 

19.  tarsalia  4  and  5  fused. 

20.  first  metatarsal 

21.  fifth  metatarsal. 

i,  ii,  in,  iv,  v,  digits. 


THE   SKELETON   OF   THE   TURTLE.      PELVIC   GIRDLE.      235 

a  horny  claw  ;  those  of  the  other  digits  are  flattened  and  more 
or  less  pointed. 

THE  PELVIC  GIRDLE. 

The  pelvic  girdle  consists  of  three  bones ;  a  dorsal  bone, 
the  ilium,  an  anterior  ventral  bone,  the  pubis,  and  a  pos- 
terior ventral  bone,  the  ischium.  All  three  bones  contribute 
largely  to  the  formation  of  the  acetabulum,  with  which  the 
head  of  the  femur  articulates. 

The  ilium  is  a  small  slightly  curved  bone,  which  unites 
ventrally  with  the  pubis  and  ischium,  and  extends  dorsal  wards 
and J^ack  wards  to  meet  the  distal  ends  of  the  sacral  ribs. 

The  pubis  is  the  largest  bone  of  the  three ;  its  distal 
end  forms  a  wide  bilobed  plate,  the  inner  lobe  meeting  its 
fellow  in  a  median  symphysis,  while  the  other  lobe  or  lateral 
process  extends  outwards.  Attached  to  the  symphysis  in  front 
is  a  cartilaginous  epipubis,  while  behind,  the  two  pubes  are 
terminated  by  a  wide  rounded  cartilaginous  area. 

The  ischium,  the  smallest  bone  of  the  three,  is  flattened 
and  like  the  pubis  meets  its  fellow  in  a  median  symphysis. 
A  narrow  band  of  cartilage  connects  the  symphysis  pubis  with 
the  symphysis  ischii,  and  separates  the  two  obturator  fora- 
mina from  one  another. 

THE  POSTERIOR  LIMB. 

This  is  divisible  into  three  portions,  the  thigh,  the  crus  or 
shin,  and  the  pes. 

The  thigh  includes  a  single  bone,  the  femur. 

The  femur  (fig.  40,  B,  12)  is  a  short  thick  bone,  with  a 
prominent  rounded  head  articulating  with  the  acetabulum. 
Behind  this  head  is  a  deep  pit,  beyond  which  is  a  roughened 
area  corresponding  with  the  great  trochanter  of  mammals. 
The  distal  end  is  expanded  and  somewhat  convex. 

The  bones  of  the  crus  or  shin  are  the  tibia  and 
fibula.  These  are  both  straight  rod -like  bones  with  expanded 


236          THE  VERTEBRATE  SKELETON. 

terminations  which  closely  approach  one  another,  while  else- 
where the  bones  diverge  considerably. 

The  terminations  of  all  three  of  the  leg  bones  are  formed 
by  epiphyses. 

The  Pes  consists  of  the  tarsus  or  ankle,  and  the  foot, 
which  is  made  up  of  five  digits. 

The  tarsus.  The  tarsal  bones  of  the  Turtle  do  not  retain 
their  primitive  arrangement  to  such  an  extent  as  do  the 
carpals.  They  are  arranged  in  a  proximal  row  of  two  and  a 
distal  row  of  four.  Of  the  bones  in  the  proximal  row  the 
postaxial  one  is  much  the  smaller  and  is  the  fibulare ;  the 
larger  pre-axial  one  (fig.  40,  B,  15)  represents  the  tibiale, 
intermedium,  and  centrale  fused,  and  articulates  with  both 
tibia  and  fibula.  The  first  three  distal  tarsalia  are  all  small 
bones  and  are  very  similar  in  size,  and  each  articulates  regu- 
larly with  the  corresponding  metatarsal.  The  fourth  bone 
(fig.  40,  B,  19)  is  much  larger,  and  represents  tarsalia  4  and  5 
fused.  The  first  two  distal  tarsalia  articulate  with  the  pre- 
axial  tarsal  of  the  proximal  row,  the  third  only  with  its  neigh- 
bours the  second,  and  the  fused  fourth  and  fifth.  The  latter 
articulates  with  both  bones  of  the  proximal  row. 

Each  digit  consists  of  a  metatarsal  and  of  a  varying  num- 
ber of  phalanges. 

The  metatarsals.  The  first  metatarsal  (fig.  40,  B,  20) 
is  broad  and  flattened,  the  second,  third  and  fourth,  are  all 
elongated  bones  with  nearly  flat  terminations  formed  by  small 
epiphyses/  The  fifth  is  large  and  flattened,  and  the  articular 
surface  for  the  phalanx  is  situated  somewhat  laterally. 

The  phalanges.  The  first  digit  has  two  phalanges  and  is 
the  stoutest  of  them  all ;  its  distal  phalanx  is  sheathed  in  a 
large  horny  claw.  The  other  digits,  of  which  the  third  is  the 
longest,  have  each  three  phalanges.  The  distal  phalanges  of 
the  second  and  third  digits  are  flattened  and  pointed  and  bear 
small  horny  claws. 


CHAPTER   XV. 
THE  SKELETON  OF  THE  CROCODILE. 

THE  species  chosen  for  description  is  C.  palustris,  a  form 
occurring  throughout  the  Oriental  region,  but  the  description 
would  apply  almost  equally  well  to  any  of  the  other  species  of 
the  genus  Crocodilus,  and  with  comparatively  unimportant 
modifications  to  any  of  the  living  Crocodilia. 

I.     EXOSKELETON. 

The  exoskeleton  of  the  Crocodile  is  strongly  developed  and 
includes  elements  of  both  epidermal  and  dermal  origin. 

a.  The  epidermal  exoskeleton  is  formed  of  a  number 
of  horny  scales  or  plates  of  variable  size  covering  the  whole 
surface  of  the  body.     Those  covering  the  dorsal  and  ventral 
surfaces  are  oblong  in  shape,  and  are  arranged  in  regular  rows 
running   transversely  across  the  body.     The    scales    covering 
the  limbs  and  head   are  mostly  smaller   and   less    regularly 
arranged,  and  are  frequently  raised  into  a  more  or  less  obvious 
keel.     Those  covering  the  dorsal  surface  of  the  tail  are  very 
prominently  keeled. 

The  epidermal  exoskeleton  also  includes  the  horny  claws 
borne  by  the  first  three  digits  of  both  manus  and  pes. 

b.  The   dermal    exoskeleton.     This   has   the   form   of 
bony   scutes  which  underlie  the  epidermal  scales  along  the 
dorsal    surface  of    the  trunk   and  anterior  part  of  the  tail. 


238          THE  VERTEBRATE  SKELETON. 

Except  in  very  young  individuals  the  epidermal  scales  are 
rubbed  off  from  these  scutes,  which  consequently  come  to  pro- 
ject freely  on  the  surface  of  the  body.  Each  scute  is  a  nearly 
square  bony  plate,  deeply  pitted  or  sculptured,  and  marked  by 
a  strong  ridge  on  its  dorsal  surface,  while  its  ventral  surface 
is  smooth.  Contiguous  scutes  are  united  to  one  another  by 
interlocking  sutures. 

The  scutes  are  arranged  in  two  distinct  areas,  viz.  (1)  a 
small  anterior  nuchal  shield  which  lies  just  behind  the  head 
and  is  formed  of  six  large  scutes  more  or  less  firmly  united 
together,  and  (2)  a  larger  posterior  dorsal  shield  covering  the 
whole  of  the  back  and  anterior  part  of  the  tail,  and  formed 
of  smaller  scutes,  which  are  arranged  in  regular  transverse 
rows,  and  progressively  diminish  in  size  when  followed  back. 

The  teeth  are  exoskeletal  structures,  partly  of  dermal, 
partly  of  epidermal  origin.  They  lie  along  the  margins  of 
the  jaws  and  are  confined  to  the  premaxillae,  maxillae  and 
dentaries.  They  are  simple  conical  structures,  without  roots  • 
each  is  in  the  adult  placed  in  a  separate  socket,  and  is  replaced 
by  another  which  as  it  grows  comes  to  occupy  the  pulp  cavity 
of  its  predecessor.  In  the  young  animal  the  teeth  are  not 
placed  in  separate  sockets  but  in  a  continuous  groove.  This 
feature  is  met  with  also  in  the  Ichthyosauria.  The  groove 
gradually  becomes  converted  into  a  series  of  sockets  by  the 
ingrowth  of  transverse  bars  of  bone.  The  anterior  teeth  are 
sharply  pointed  and  slightly  recurved,  the  posterior  ones  are 
more  blunt. 

The  upper  jaw  bears  about  nineteen  pairs  of  teeth,  the 
lower  jaw  about  fifteen  pairs.  The  largest  tooth  in  the  upper 
jaw  is  the  tenth,  and  in  the  lower  jaw  the  fourth. 

The  three  living  families  of  Crocodilia,  the  Crocodiles, 
Alligators  and  Garials,  can  be  readily  distinguished  by  the 
characters  of  the  first  and  fourth  lower  teeth.  In  Alligators 
both  first  and  fourth  lower  teeth  bite  into  pits  in  the  upper 
jaw ;  in  Garials  they  both  bite  into  notches  or  grooves  in 


SKELETON  OF  THE  CROCODILE.  VERTEBRAL  COLUMN.  239 


the  upper  jaw.     In  Crocodiles  the  first  tooth  bites  into  a  pit, 
the  fourth  into  a  notch  in  the  upper  jaw. 

II.     ENDOSKELETOK 
1.     THE    AXIAL    SKELETON. 

This  includes  the  vertebral  column,  the  skull,  and  the  ribs 
and  sternum. 

A.     THE  VERTEBRAL  COLUMN. 

The  vertebral  column  is  very  long,  consisting  of  some  sixty 
vertebrae.  It  can  be  divided  into  the  usual  five  regions,  the 
cervical,  thoracic,  lumbar,  sacral,  and  caudal  regions. 


10 


FIG.  41. 


FlKST  FOUR  CEKVICAL   VERTEBKAE    OF   A   CROCODILE    (C '. 

(Partly  after  VON  ZITTEL.) 

pro-atlas.  7.     tubercular  portion  of  fourth 

lateral  portion  of  atlas, 
odontoid  process.  8. 

ventral  portion  of  atlas.  9. 

neural  spine  of  axis.  10. 

postzygapophysis   of    fourth 
vertebra. 


cervical  rib. 
first  cervical  rib. 
second  cervical  rib. 
convex  posterior  surface   of 

centrum  of  fourth  vertebra. 


THE  CERVICAL  VERTEBRAE. 

Counting  as  cervical  all  those  vertebrae  which  are  anterior 
to  the  first  one  whose  ribs  meet  the  sternum,  there  are  nine 
cervical  vertebrae,  all  of  which  bear  ribs. 

As  a  type  of  the  cervical  vertebrae  the  fifth  may  be  taken. 


240          THE  VERTEBRATE  SKELETON. 

It  has  a  short  cylindrical  centrum  deeply  concave  in  front 
and  convex  behind.  From  the  anterior  part  of  the  ventral 
surface  of  the  centrum  arises  a  short  hypapophysis,  and 
on  each  side  is  a  facet  with  which  the  lower  limb  (capi- 
tulum)  of  the  cervical  rib  articulates.  The  neural  arch  is 
strongly  developed  and  drawn  out  dorsally  into  a  long  neural 
spine,  in  front  of  which  are  a  pair  of  upstanding  processes 
bearing  the  prominent  upwardly  and  inwardly  directed  pre- 
zygapophyses.  At  the  sides  and  slightly  behind  the  neural 
spine  are  a  corresponding  pair  of  processes  bearing  the  post- 
zygapophyses,  which  look  downwards  and  outwards.  At 
the  point  where  it  joins  the  centrum  the  neural  arch  is  drawn 
out  into  a  short  blunt  transverse  process  with  which  the 
upper  limb  (tuberculum)  of  the  cervical  rib  articulates.  The 
sides  of  the  neural  arch  are  slightly  notched  behind  for  the  exit 
of  the  spinal  nerves. 

The  first  or  atlas  vertebra  differs  much  from  any  of  the 
others,  and  consists  of  four  quite  detached  portions,  a  ventral 
arch,  with  two  lateral  portions  and  one  dorsal.  The  ventral 
arch  (fig.  41,  4)  is  flat  below  and  slightly  concave  in  front, 
forming  together  with  two  flattened  surfaces  on  the  lateral 
portions  a  large  articulating  surface  for  the  occipital  condyle 
of  the  skull.  Its  posterior  face  is  bevelled  off  and  forms  with 
a  second  pair  of  facets  on  the  lateral  portions  a  surface  with 
which  the  odontoid  process  of  the  second  vertebra  articulates. 
The  postero-lateral  surfaces  of  the  ventral  arch  also  bear  a  pair  of 
little  facets  with  which  the  cervical  ribs  articulate.  The  lateral 
portions  are  somewhat  flattened  and  expanded,  and  bear  in  ad- 
dition to  those  previously  mentioned  a  pair  of  small  downwardly 
directed  facets,  the  postzygapophyses,  which  articulate  with  the 
prezygapophyses  of  the  second  vertebra.  The  dorsal  portion 
(fig.  41,  1)  is  somewhat  triangular  in  shape,  and  overhangs  the 
occipital  condyle.  It  is  often  regarded  as  the  neural  arch  of  a 
vertebra  in  front  of  the  atlas  and  is  called  the  pro-atlas  ;  but 
as  it  is  a  membrane  bone  it  is  not  properly  a  vertebral  element. 


SKELETON  OF  THE  CROCODILE.      VERTEBRAL  COLUMN.      241 

The  second  or  axis  vertebra  also  differs  a  good  deal  from 
the  other  cervicals.  The  centrum  is  massive,  and  is  terminated 
in  front  by  a  very  large  slightly  concave  articulating  surface 
formed  by  the  odontoid  process  (fig.  41,  3)  which  is  united 
with  the  centrum  by  suture  only,  and  is  really  the  detached 
centrum  of  the  first  vertebra.  The  cervical  rib  (fig.  41,  9) 
articulates  with  two  little  irregularities  on  the  odontoid  pro- 
cess. The  posterior  surface  of  the  centrum  is  convex.  The 
neural  arch  is  strongly  developed  and  terminated  dorsally 
by  a  long  neural  spine  (fig.  41,  5),  its  sides  are  notched, 
slightly  in  front  and  more  prominently  behind  for  the  exit  ofr 
the  spinal  nerves.  It  is  drawn  out  in  front  into  two  little 
processes  bearing  a  pair  of  upwardly  and  outwardly  directed 
prezygapophyses,  while  the  postzygapophyses  are  similar  to 
those  of  the  other  cervical  vertebrae. 

The  last  two  cervical  vertebrae  resemble  the  succeeding 
thoracic  vertebrae,  in  the  increased  length  of  the  transverse 
processes,  and  the  shifting  dorsalwards  of  the  facet  with  which 
the  capitulum  of  the  rib  articulates. 

THE  THORACIC  VERTEBRAE. 

The  thoracic  vertebrae  commence  with  the  first  of  those 
that  bears  ribs  reaching  the  sternum.  They  are  ten  in 
number,  and  the  first  eight  are  directly  connected  with  the 
sternum  by  ribs. 

The  third  of  them  may  be  taken  as  a  type.  It  has  a 
thick  cylindrical  centrum,  concave  in  front  and  convex  behind, 
there  is  a  slight  hypapophysis,  and  the  centrum  is  suturally 
united  with  a  strong  neural  arch  enclosing  a  narrow  neural 
canal.  The  neural  arch  is  drawn  out  dorsally  into  a  wide 
truncated  neural  spine,  and  laterally  into  two  prominent 
transverse  processes,  with  the  ends  of  which  the  tubercula  of 
the  ribs  articulate,  while  the  capitulum  articulates  in  each  case 
with  a  step-like  facet  (fig.  42,  A,  3)  on  the  anterior  face  of  the 
transverse  process.  The  prezygapophyses  (fig.  42,  A,  2)  are 
R.  16 


242 


THE  VERTEBRATE  SKELETON. 


borne  on  outgrowths  from  the  bases  of  the  transverse  pro- 
cesses, and  the  postzygapophyses  on  outgrowths  at  the  base  of 
the  neural  spine. 

The  thoracic  vertebrae  behind  the  third  have  no  hypa- 
pophyses,  and  the  capitular  facets  gradually  come  to  be  placed 
nearer  and  nearer  the  ends  of  the  transverse  processes,  at  the 
same  time  becoming  less  prominent ;  otherwise  these  vertebrae 
are  just  like  the  third. 

A  B 


FIG.  42.     ANTERIOR  VIEW  OF  A,  A  LATE  THOBACIC  AND  B,  THE  FIKST  SACRAL 

VERTEBRA   OF    A    YOUNG    CROCODILE    (C.   palustris).        X  ^. 

1.     neural  spine.  4.     sacral  rib. 

5.     surface  which  is  united  with 
the  ilium. 


neural  spine. 

process     bearing    prezygapo- 

physis. 
facet  for  articulation  with  the 

capitulum  of  the  rib. 


6. 


concave  anterior  face  of  cen- 
trum. 


In  the  first  and  second  thoracic  vertebrae  the  capitulum  of 
the  rib  articulates,  not  with  a  facet  on  the  transverse  process, 
but  with  a  little  elevation  borne  at  the  line  of  junction  of  the 
centrum  and  neural  arch. 

THE  LUMBAR  VERTEBRAE. 

These  are  five  in  number,  and  are  precisely  like  the 
posterior  thoracic  vertebrae,  except  in  the  fact  that  the 
transverse  processes  have  no  facets  for  the  articulation  of  ribs. 


SKELETON  OF  THE  CROCODILE.   VERTEBRAL  COLUMN.   243 

THE  SACRAL  VERTEBRAE. 

These  are  two  in  number,  and  while  the  centrum  of  the 
first  is  concave  in  front  (fig.  42,  B,  6)  and  nearly  flat  behind, 
that  of  the  second  is  flat  in  front  and  concave  behind.  Each 
has  a  pair  of  strong  ribs  (fig.  42,  B,  4)  firmly  ankylosed  in  the 
adult  with  a  wide  surface  furnished  partly  by  the  centrum, 
partly  by  the  neural  arch.  The  distal  ends  of  these  ribs  are 
united  with  the  ilia.  The  character  of  the  neural  spines  and 
zygapophyses  is  the  same  as  in  the  thoracic  vertebrae. 

THE  CAUDAL  VERTEBRAE. 

These  are  very  numerous,  about  thirty-four  in  number. 
The  first  differs  from  all  the  other  vertebrae  of  the  body  in 
having  a  biconvex  centrum.  The  succeeding  ones  are  procoe- 
lous  and  are  very  much  like  the  posterior  thoracic  and  lumbar 
vertebrae,  having  high  neural  spines  and  prominent  straight 
transverse  processes.  They  differ  however  in  having  the 
neural  spines  less  strongly  truncated  above,  and  the  transverse 
processes  arise  from  the  centra  and  not  from  the  neural 
arches.  When  followed  further  back  the  centra  arid  neural 
spines  gradually  lengthen  while  the  transverse  processes  be- 
come reduced,  and  after  the  twelfth  vertebra  disappear. 
Further  back  still  the  neural  spines  and  zygapophyses 
gradually  become  reduced  and  disappear,  as  finally  the  neural 
arch  does  also,  so  that  the  last  few  vertebrae  consist  simply  of 
cylindrical  centra. 

Each  caudal  vertebra,  except  the  first  and  the  last  eleven 
or  so,  has  a  V-shaped  chevron  bone  attached  to  the  postero- 
ventral  edge  of  its  centrum.  The  anterior  ones  are  the  largest 
and  they  gradually  decrease  in  size  till  they  disappear. 

B.     THE  SKULL1. 

The  skull  of  the  Crocodile  is  a  massive  depressed  structure 

1  Free  use  has  been  made  of  L.  C.  MialPs  Studies  in  Comparative 
Anatomy,  i.,  The  Skull  in  Crocodilia,  London,  1878.  See  also  W.  K. 
Parker,  Tr.  Z.  S.t  vol.  xi.  1885,  p.  263. 

16—2 


244          THE  VERTEBRATE  SKELETON. 

presenting  a  number  of  striking  characteristics,  some  of  the 
more  important  of  which  are  : — 

1.  All  the  bones  except  the  mandible,  hyoid,  and  columella 
are  fir  inly  united  by  interlocking  sutures.     In  spite  of  this, 
however,  growth  of  the  whole  skull  and  of   the  component 
bones  goes  on  continuously  throughout  life,  this  growth  being 
especially  marked  in  the  case  of  the  facial  as  opposed  to  the 
cranial  part  of  the  skull. 

2.  All    the   bones    appearing   on  the  dorsal  surface  are 
remarkable  for  their  curious  roughened  and  pitted  character ; 
this  feature  is  prominent  also  in.  many  Labyrinthodonts. 

3.  The  size  of  the  jaws  and  teeth  is  very  great. 

4.  The  mandibular  condyle  is  carried  back  to  some  dis- 
tance behind  the  occipital  condyle. 

5.  The  occipital  plane  (see  p.  386)  of  the  skull  is  vertical. 

6.  The  length  of  the  secondary  palate  is  remarkably  great, 
and  the  vomer  takes  no  part  in  its  formation. 

7.  The  posterior  nares  are  placed  very  far  back,  the  nasal 
passages  being  as  in  mammals  separated  from  the  mouth  by 
the  long  secondary  palate. 

8.  There  is  a  complicated  system  of  Eustachian  passages 
communicating  at  one  end  with  the  tympanic  cavity  and  at 
the  other  end  with  the  mouth  cavity. 

9.  The  interorbital   septum   is  mainly  cartilaginous,  the 
presphenoidal    and    orbitosphenoidal    regions    remaining   un- 
ossified. 

The  skull  is  divisible  into  three  parts  : — 

(1)  the  cranium,  (2)  the  lower  jaw,  (3)  the  hyoid. 

The  cranium  may  again  for  purposes  of   description  be 
divided  into  :-<- 

1.  the  cranium  proper  or  brain  case ; 

2.  the   bones    connected    with    the    several    special    sense 
organs ; 

3.  the  bones  of  the  upper  jaw,  and  suspensorial  apparatus. 


SKELETON  OF  THE  CROCODILE.   THE  SKULL.   245 


1.     THE  CRANIUM  PROPER  OR  BRAIN  CASE. 

The  cartilage  and  membrane  bones  of  the  cranium  proper 

A  B 


FIG. 

1. 
2. 

3. 
4. 
5. 

6. 
7. 
8. 
9. 
10. 

11. 


43.     PALATAL  ASPECT  A,  OF  THE  CRANIUM,  B,  or  THE  MANDIBLE  OF 
AN  ALLIGATOR  (Caiman  latirostris).     x  -|.     (Brit.  Mus.) 


premaxilla.  12. 

maxilla.  13. 

palatine.  14. 

pterygoid.  15. 

posterior  nares.  16. 

transpalatine.  17. 

posterior  palatine  vacuity.  18. 

anterior  palatine  vacuity.  19. 

basi-occipital.  20. 
opening    of    median    Eusta-       21. 

chian  canal, 
jugal. 


quadratojugal. 
quadrate, 
dentary. 
splenial. 
coronoid. 
supra-angular, 
angular, 
articular. 

lateral  temporal  fossa.  • 
openings   of  vascular  canals 
leading  into  alveolar  sinus. 


246          THE  VERTEBRATE  SKELETON. 

when  taken  together  can  in  most  vertebrates  be  seen  to  be 
more  or  less  arranged  in  three  rings  or  segments  called  respec- 
tively the  occipital,  parietal  and  frontal  segments ;  in  the 
Crocodile  however  only  the  occipital  and  parietal  segments 
are  clearly  seen. 

The  occipital  segment  consists  of  four  cartilage  bones, 
three  of  which  together  surround  the  foramen  magnum. 

The  most  ventral  of  these,  the  basi-occipital  (figs.  43 
and  45,  9),  forms  the  single  convex  occipital  condyle  for 
articulation  with  the  atlas,  bounds  the  base  of  the  foramen 
magnum,  and  is  continuous  laterally  with  two  larger  bones, 
the  exoccipitals  (fig.  45,  24),  which  meet  one  another  dor- 
sally  and  form  the  remainder  of  the  boundary  of  the  foramen 
magnum.  Each  is  drawn  out  externally  into  a  strong  process, 
which  is  united  below  with  the  quadrate,  and  above  with  the 
squamosal  by  a  surface  seen  in  a  disarticulated  skull  to  be 
very  rough  and  splintered.  In  a  longitudinal  section  the 
anterior  face  of  the  exoccipital  is  seen  to  be  closely  united 
with  the  opisthotic. 

The  exoccipital  is  pierced  by  a  number  of  foramina,  four 
lying  on  the  posterior  surface.  Just  external  to  the  foramen 
magnum  is  a  small  foramen  for  the  exit  of  the  hypoglossal 
nerve  (figs.  44  and  45,  XII).  External  to  this  is  the  foramen 
for  the  pneumogastric  (fig.  44,  X),  while  more  ventrally  still 
is  the  foramen  (fig.  44,  15)  through  which  the  internal  carotid 
artery  enters  the  skull.  Some  distance  further  to  the  side, 
and  more  dorsally,  is  a  larger  foramen  which  gives  passage 
to  the  facial  nerve  and  certain  blood-vessels. 

In  a  median  longitudinal  section  of  the  skull  the  hypo- 
glossal  foramen  is  seen,  and  just  in  front  of  it  a  small  foramen 
for  a  vein.  Further  forwards  the  long  slit-like  opening 
between  the  exoccipital  and  opisthotic  is  the  internal  audi- 
tory meatus  (fig.  45,  VIII)  through  which  the  auditory 
nerve  leaves  the  cranial  cavity  and  enters  the  internal 
ear. 


SKELETON  OF  THE  CKOCODILE.   THE  CRANIUM.  247 

The  supra-occipital  (fig.  45,  5)  is  a  small  bone  which 
takes  no  part  in  the  formation  of  the  foramen  magnum,  and  is 
closely  united  in  front  with  the  epi-otic.  It  is  characteristic  of 
Crocodiles  that  all  the  bones  of  the  occipital  segment  have 
their  longer  axes  placed  vertically,  and  that  they  scarcely  if  at 
all  appear  on  the  dorsal  surface. 

In  front  of  the  occipital  segment  is  the  parietal  segment. 
The  dorsal  and  ventral  portions  of  the  two  segments  are  in 
contact  with  one  another,  but  the  lateral  portions  are  widely 
separated  by  the  interposition  of  the  auditory  and  suspen- 
sorial  bones. 

The  basisphenoid  (fig.  45,  12)  is  an  unpaired  wedge- 
shaped  bone,  united  along  a  deep  vertical  suture  with  the  basi- 
occipital.  The  two  bones  are,  however,  partially  separated  in 
the  mid-ventral  line  by  a  foramen,  the  opening  of  the  median 
Eustachian  canal,  which  leads  into  a  complicated  system  of 
Eustachian  passages  ultimately  communicating  with  the  tym- 
panic cavity. 

The  dorsal  surface  of  the  basisphenoid  is  well  seen  in  a 
section  of  the  skull,  but  owing  to  the  way  it  tapers  ventrally, 
it  appears  on  the  ventral  surface  only  as  a  very  narrow  strip 
of  bone  wedged  in  between  the  basi-occipital  and  pterygoids. 
In  a  lateral  view  it  is  seen  to  be  drawn  out  in  front  into  an 
abruptly  truncated  process,  the  rostrum,  which  forms  part  of 
the  interorbital  septum.  On  the  anterior  part  of  the  dorsal 
surface  is  a  deep  pit,  the  pituitary  fossa  or  sella  turcica, 
at  the  base  of  which  are  a  pair  of  foramina,  through  which 
the  carotid  arteries  pass.  Dorso-laterally  the  basisphenoid 
articulates  with  the  alisphenoids. 

The  alisphenoids  (fig.  45, 13)  are  a  pair  of  irregular  bones 
which  arise  from  the  basisphenoid  antero-laterally,  and  are 
united  dorsally  with  the  parietal,  frontal,  and  postfrontals. 
They  bound  most  of  the  anterior  part  of  the  brain  case, 
and  each  presents  on  its  inner  face  a  deep  concavity  which 
lodges  the  cerebral  hemisphere  of  its  side.  Viewed  from 


248 


THE  VERTEBRATE  SKELETON. 


8  S 1  8  f  o  &  § 

PH  g  45  ft-S,  ft  M  0< 


SKELETON  OF  THE  CROCODILE.   THE  CRANIUM.   249 

the  ventral  side  the  two  alisphenoids  are  seen  to  almost 
or  quite  meet  one  another  immediately  below  the  frontal, 
and  then  to  diverge,  forming  an  irregular  opening — partially 
closed  by  cartilage  in  the  fresh  specimen, — through  which 
the  optic  nerves  leave  the  cranial  cavity.  Further  back  the 
alisphenoids  meet  one  another  for  a  narrow  area,  and  then 
diverge  again,  so  that  between  each  and  the  rostrum  of 
the  basisphenoid  there  appears  an  opening  (fig.  44,  III,  YI) 
through  which  the  oculomotor  and  abducens  nerves  leave 
the  cranium.  Further  back  still  each  is  united  for  a  short 
space  with  the  basisphenoid,  pterygoid  and  quadrate,  and 
then  becomes  separated  from  the  quadrate  by  a  large  foramen, 
the  foramen  ovale  (fig.  44,  Y),  through  which  the  whole  of 
the  trigeminal  nerve  passes  out. 

The  dorsal  portion  of  the  parietal  segment  is  formed  by 
the  parietal  (fig.  45,  4),  which  though  double  in  the  embryo, 
early  comes  to  form  a  single  bone.  It  extends  over  the 
posterior  part  of  the  cranial  cavity,  and  is  continuous  in  front 
with  the  frontal,  behind  with  the  supra-occipital,  and  laterally 
with  the  postfrontals,  squamosals,  alisphenoids,  pro-otics  and 
epi-otics.  It  forms  the  inner  boundary  of  a  large  rounded 
vacuity  on  the  roof  of  the  skull,  the  supratemporal  fossa. 

The  frontal  segment  is  very  imperfectly  ossified,  there 
being  no  certain  representatives  of  either  the  ventral  member, 
the  presphenoid,  or  the  lateral  members,  the  orbitosphenoids. 
On  the  dorsal  side  there  is,  however,  a  large  development 
of  membrane  bones.  There  is  a  large  frontal  (fig.  45,  3), 
unpaired,  except  in  the  embryo,  united  behind  with  the 
parietal  and  postfrontal,  and  drawn  out  in  front  into  a  long 
process  which  is  overlapped  by  the  prefrontals  and  posterior 
part  of  the  nasals.  The  frontal  ends  off  freely  below,  owing 
to  the  orbitosphenoidal  region  being  unossified,  it  forms  a 
considerable  part  of  the  roof  of  the  cranial  cavity,  but  takes 
no  part  in  the  formation  of  the  wall. 

Each  prefrontal  (fig.  45,  14)  forms  part  of  the  inner  wall 


250          THE  VERTEBRATE  SKELETON. 

of  the  orbit  and  sends  veiitralwards  a  process  which  meets 
the  palatine. 

The  postfrontals  (fig.  44,  6)  are  small  bones  lying  at  the 
sides  of  the  posterior  part  of  the  frontal.  Each  is  united 
with  a  number  of  bones,  on  its  inner  side  with  the  frontal  and 
parietal,  behind  with  the  squamosal,  and  ventrally  with  the 
alisphenoid.  It  also  unites  by  means  of  a  strong  descending 
process  with  an  upgrowth  from  the  jugal,  and  thus  forms  a 
postorbital  bar  separating  the  orbit  from  the  lateral  tem- 
poral fossa.  The  postfrontal  forms  also  part  of  the  outer 
boundary  of  the  supratemporal  fossa. 

2.     THE  SENSE  CAPSULES. 

Skeletal  capsules  occur  in  connection  with  each  of  the  three 
special  sense  organs  of  sight,  of  hearing  and  of  smell. 

The  Auditory  capsules  and  associated  bones. 

Three  bones,  the  epi-otic,  opisthotic  and  pro-otic, 
together  form  the  auditory  or  periotic  capsule  of  each  side. 
They  are  wedged  in  between  the  lateral  portions  of  the  occi- 
pital and  parietal  segments  and  complete  the  cranial  wall  in 
this  region.  Their  relations  to  the  surrounding  structures  are 
very  complicated,  and  many  points  can  be  made  out  only  in 
sections  of  the  skull  passing  right  through  the  periotic  cap- 
sule. The  relative  position  of  the  three  bones  is,  however, 
well  seen  in  a  median  longitudinal  section.  The  opisthotic 
early  becomes  united  with  the  exoccipital,  while  the  epi-otic 
similarly  becomes  united  with  the  supra-occipital,  the  pro- 
otic  (fig.  45,  7), — seen  in  longitudinal  section  to  be  pierced 
by  the  prominent  trigeminal  foramen — alone  remaining 
distinct  throughout  life.  The  three  bones  together  surround 
the  essential  organ  of  hearing  which  communicates  laterally 
with  the  deep  tympanic  cavity  by  the  fenestra  ovalis. 

The  tympanic  cavity,  leading  to  the  exterior  by  the 
external' auditory  meatus  (fig.  44,  16),  is  well  seen  in  a 


SKELETON    OF   THE    CROCODILE.      SENSE   CAPSULES.      251 

side-view  of  the  skull ;  it  is  bounded  on  its  inner  side  by  the 
periotic  bones,  posteriorly  in  part  by  the  exoccipital,  and  else- 
where mainly  by  the  quadrate.  A  large  number  of  canals 
and  passages  open  into  it.  On  its  inner  side  opening  ventro- 
anteriorly  is  the  fenestra  ovalis,  opening  ventro-posteriorly 
the  internal  auditory  meatus  (fig.  45,  \TIII),  while  dorsally 
there  is  a  wide  opening  which  forms  a  communication  through 
the  roof  of  the  brain-case  with  the  tympanic  cavity  of  the 
other  side.  On  its  posterior  wall  is  the  prominent  foramen 
through  which  the  facial  nerve  passes  on  its  way  to  its  final 
exit  from  the  skull  through  the  exoccipital,  this  foramen  is 
bounded  by  the  quadrate,  squamosal,  and  exoccipital. 

The  opening  of  the  fenestra  ovalis  is  in  the  fresh  skull 
occupied  by  the  expanded  end  of  the  auditory  ossicle,  the 
columella,  whose  outer  end  articulates  by  a  concave  facet 
with  a  trifid  extracolumellar  cartilage  which  reaches  the 
tympanic  membrane.  The  lower  process  of  this  extracolumella 
passes  into  a  cartilaginous  rod  which  lies  in  a  canal  in  the 
quadrate  and  is  during  life  continuous  with  Meckel's  cartilage 
within  the  articular  bone  of  the  mandible. 

The  columella  and  extracolumella  are  together  homologous 
with  the  chain  of  mammalian  auditory  ossicles. 

The  Optic  capsules  and  associated  bones. 

Two  pairs  of  bones  are  associated  with  the  optic  capsules, 
viz.  the  lachrymals  and  the  supra-orbitals.  The  lachrymal 
(fig.  44,  3)  is  a  fairly  large  flattened  bone  lying  wedged  in 
between  the  maxilla,  nasal,  jugal,  and  prefrontal.  It  forms  a 
considerable  part  of  the  anterior  boundary  of  the  orbit,  and  is 
pierced  by  two  foramina.  On  the  orbital  edge  is  a  large  hole 
leading  into  a  cavity  within  the  bone  which  lodges  the  naso- 
lachrymal  sac,  and  communicates  with  the  narial  passage  by 
a  wide  second  foramen  near  the  anterior  end  of  the  bone. 
The  supra-orbital  is  a  very  small  loose  bone  lying  in  the  eyelid 
close  to  the  junction  of  the  frontal  and  prefrontal. 


252  THE   VERTEBRATE   SKELETON. 

The  Olfactory  capsules  and  associated  bones. 

Two  pairs  of  membrane  bones,  the  vomers  and  nasals,  are 
developed  in  association  with  the  olfactory  organ,  but  the 
mesethmoid  is  not  ossified. 

The  vomers  form  a  pair  of  delicate  bones,  each  consisting  of 
a  vertical  plate  (fig.  45,  15),  which  with  its  fellow  separates 
the  two  narial  passages,  and  of  a  horizontal  plate  which  forms 
much  of  their  roof.  The  vomers  articulate  with  one  another 
and  with  the  pterygoids,  palatines,  and  maxillae. 

The  nasals  (fig.  45,  2)  are  very  long  narrow  bones  extend- 
ing along  the  middle  line  from  the  frontal  almost  to  the 
anterior  nares.  They  are  continuous  laterally  with  the  pre- 
maxillae,  maxillae,  lachrymals  and  prefrontals.  They  form 
the  roof  of  the  narial  passages. 

3.     THE  UPPER  JAW  AND  SUSPENSORIAL  APPARATUS. 

These  are  enormously  developed  in  the  Crocodile  and  are 
firmly  united  to  the  cranium.  It  will  be  most  convenient  to 
begin  by  describing  the  bones  at  the  anterior  end  of  the  jaw 
and  to  work  back  thence  towards  the  brain-case.  The  most 
anterior  bones  are  the  premaxillae.  The  premaxillae  (figs.  44 
and  45,  1)  are  small  bones,  each  bearing  five  pairs  of  teeth, 
set  in  separate  sockets  in  their  alveolar  borders.  They  con- 
stitute almost  the  whole  of  the  boundary  of  the  anterior 
nares,  which  are  confluent  with  one  another  and  form  a 
large  semicircular  opening  in  the  roof  of  the  skull,  leading 
into  the  wide  narial  passage.  They  are  also  partially  sepa- 
rated from  one  another  in  the  ventral  middle  line,  by  the 
small  anterior  palatine  vacuity  (fig.  43,  A,  8).  They  form 
the  anterior  part  of  the  broad  palate.  The  alveolar  border 
on  each  side  between  certain  of  the  teeth  is  marked  by  pits 
which  receive  the  points  of  the  teeth  of  the  other  jaw.  The 
first  pair  of  these  pits  in  the  premaxillae  are  often  so  deep  as 
to  be  converted  into  perforations.  Pits  of  the  same  character 
occur  between  the  maxillary  and  mandibular  teeth. 


THE    SKELETON   OF   THE   CROCODILE.  253 

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254  THE   VERTEBRATE   SKELETON. 

The  maxillae  (figs.  43,  A,  2  and  44,  2)  are  a  pair  of  very 
large  bones  and  bear  the  remaining  teeth  of  the  upper  jaw, 
set  in  sockets  along  their  alveolar  borders.  On  the  dorsal 
side  each  maxilla  is  continuous  with  the  premaxilla,  nasal, 
lachrymal,  and  jugal,  while  ventrally  it  meets  its  fellow  in  a 
long  straight  suture  and  forms  the  greater  part  of  the  long- 
bony  palate.  The  maxillae  are  separated  in  the  middle  line 
posteriorly  by  processes  from  the  palatines,  while  further  back 
they  meet  the  transpalatines.  The  internal  or  nasal  surface, 
like  that  of  the  premaxilla,  is  excavated  by  a  deep  longitudi- 
nal groove,  the  narial  passage.  In  a  ventral  view  of.  the 
skull  a  number  of  small  openings  (fig.  43,  A,  21)  are  seen 
close  to  the  alveolar  border,  these  are  the  openings  of  small 
vascular  canals  which  lead  into  the  alveolar  sinus,  a  passage 
traversing  the  maxilla,  and  transmitting  the  superior  max- 
illary branch  of  the  trigeminal  nerve  and  certain  blood-vessels. 
This  alveolar  sinus  opens  posteriorly  by  the  more  external  of 
the  two  large  holes  in  the  maxilla,  which  lie  close  to  the 
anterior  edge  of  the  posterior  palatine  vacuity,  to  be  described 
immediately.  The  more  internal  of  these  holes,  on  the  other 
hand,  leads  into  a  cavity  lodging  the  nasal  sac.  Behind  the 
maxillae  the  completeness  of  the  palate  is  broken  up  by  the 
large  oval  posterior  palatine  vacuities  (fig.  43,  A,  7) ; 
these  are  separated  from  one  another  in  the  middle  line  by  the 
palatines,  and  are  bounded  elsewhere  by  the  maxillae,  trans- 
palatines,  and  pterygoids. 

The  palatines  (fig.  43,  A,  3)  are  long  and  rather  narrow 
bones  interposed  between  the  maxillae  in  front  and  pterygoids 
behind.  They  meet  one  another  in  a  long  suture  and  form 
much  of  the  posterior  part  of  the  palate,  while  the  whole  length 
of  their  dorsal  surface  contributes  to  the  floor  of  the  narial 
passage.  The  dorsal  surface  of  each  bone  is  also  drawn  out 
on  its  outer  side  into  a  prominent  ridge  which  forms  much  of 
the  side  and  roof  of  the  narial  passage,  being  in  contact  with 
the  vomer  and  pterygoid,  and  at  one  point  by  means  of  a  short 


SKELETON  OF  THE  CROCODILE.   THE  SKULL.   255 

ascending  process  with  the  descending  process  of  the  pre- 
f  rental. 

The  pterygoids  (tigs.  43,  A,  4,  and  45,  11)  are  a  pair  of 
large  bones,  each  consisting  of  a  median  more  or  less  vertical 
part,  which  becomes  ankylosed  to  its  fellow  in  the  middle 
line  early  in  life,  and  of  a  wide  horizontal  part  which  meets 
the  transpalatine.  They  completely  surround  the  posterior 
nares  (fig.  43,  A,  5)  and  their  median  portions  form  the  whole 
boundary  of  the  posterior  part  of  the  narial  passage,  and  assist 
the  palatines  and  vomers  in  bounding  the  middle  part.  'The 
horizontal  parts  form  the  posterior  part  of  the  secondary  palate, 
while  the  dorsal  surface  of  each  looks  into  the  pterygoid  fossa, 
a  large  cavity  lying  below  the  quadrate  and  quadratojugal  at 
the  side  of  the  skull.  The  lateral  margin  adjoining  the  trans- 
palatine  is  in  the  fresh  skull  terminated  by  a  plate  of  cartilage 
against  which  the  mandible  plays.  Dorsally  the  pterygoid 
articulates  with  the  basisphenoid,  quadrate,  and  alisphenoid. 

The  transpalatines  (fig.  44,  11)  connect  the  pterygoids  with 
the  jugals  and  maxillae,  articulating  with  each  of  the  three 
bones  by  a  long  pointed  process.  The  jugal  process  meets  also 
a  down-growth  from  the  postfrontal. 

The  jugals  or  molars  (fig.  44,  5)  are  long  somewhat  flat- 
tened bones  which  are  united  to  the  lachrymals  and  maxillae 
in  front,  while  passing  backwards  each  is  united  behind  to  the 
quadratojugal  (fig.  44,  12),  the  two  forming  the  infratemporal 
arcade  which  constitutes  the  external  boundary  of  the  orbit 
and  lateral  temporal  fossa.  The  jugal  is  united  below  to  the 
transpalatine,  and  the  two  bones  together  form  an  outgrowth, 
which  meeting  that  from  the  postfrontal  forms  the  postorbital 
bar,  and  separates  the  orbit  from  the  lateral  temporal  fossa. 
The  quadratojugals  are  small  bones  and  are  united  behind 
with  the  quadrates. 

The  quadrate  (figs.  43,  A,  13  and  44,  8)  of  each  side  is 
a  large  somewhat  flattened  bone  firmly  fixed  in  among  the 
other  bones  of  the  skull.  It  is  terminated  posteriorly  by  an 


256  THE   VERTEBRATE   SKELETON. 

elongated  slightly  convex  surface,  coated  with  cartilage  in  the 
fresh  skull,  by  which  the  mandible  articulates  with  the  cranium. 
The  dorsal  surface  of  the  quadrate  is  flat  behind,  further  for- 
wards it  becomes  much  roughened  and  articulates  with  the 
exoccipital  and  squamosal ;  further  forwards  still  it  becomes 
marked  by  a  deep  groove  which  forms  "the  floor  of  the  ex- 
ternal auditory  meatus  and  part  of  the  tympanic  cavity. 
The  anterior  boundary  of  the  quadrate  is  extremely  irregu- 
lar, it  is  united  dorsally  with  the  postfrontal,  pro-otic,  and 
squamosal,  and  more  ventrally  with  the  alisphenoid.  The 
smooth  ventral  surface  looks  into  the  pterygoid  fossa.  In 
front  the  quadrate  forms  the  posterior  boundary  of  the  supra- 
temporal  fossa  and  foramen  ovale,  and  is  continuous  with  the 
alisphenoid,  while  it  sends  down  a  thin  plate  meeting  the 
pterygoid  and  basisphenoid.  On  the  inner  side  of  the  dorsal 
surface  of  the  quadrate  near  the  condyle,  is  a  small  foramen 
which  leads  into  a  tube  communicating  with  the  tympanic 
cavity,  by  a  foramen  lying  in  front  of  and  ventral  to  that  for 
the  exit  of  the  facial  nerve.  By  this  tube  air  can  pass  from 
the  tympanic  cavity  into  the  articular  bone  of  the  mandible. 

The  squamosal  (fig.  44,  7)  meets  the  quadrate  and  exoccipital 
below,  and  forms  part  of  the  roof  of  the  external  auditory 
meatus,  while  above  it  forms  part  of  the  roof  of  the  skull  and 
has  a  pitted  structure  like  that  of  the  other  bones  of  the  roof. 
It  is  continuous  with  the  postfrontal  in  front,  forming  with 
it  the  supratemporal  arcade  which  constitutes  the  outer 
boundary  of  the  supratemporal  fossa.  It  meets  also  the 
parietal  on  its  inner  side,  forming  the  post-temporal  bar,  the 
posterior  boundary  of  the  supratemporal  fossa. 

It  may  be  useful  to  recapitulate  the  large  vacuities  in  the 
surface  of  the  Crocodile's  cranium. 

Dorsal  surface. 

1.  The  Supratemporal  fossae.  Each  is  bounded  in- 
ternally by  the  parietal,  behind  by  the  post-temporal  bar 
formed  by  the  parietal  and  squamosal,  and  externally  by  the 


SKELETON  OF  THE  CROCODILE.   THE  SKULL.    257 

supratemporal  arcade  formed  by  the  squamosal  and  post- 
frontal.  The  postf  rontal  meets  the  parietal  in  front  and  forms 
the  anterior  boundary  of  the  supratemporal  fossa. 

2.  The   Lateral  temporal  or  infratemporal   fossae. 
These  lie  below  and  to  the  outer  side  of  the  supratemporal 
fossae.    Each  is  bounded  dorso-internally  by  the  supratemporal 
arcade  ;  and  behind  by  a  continuation  of  the  post-temporal  bar 
formed    by    the    quadrate    and    quadratojugal.     The  external 
boundary  is  the  infratemporal  arcade  formed  of  the  quad- 
ratojugal and  jugal,  while  in  front  the  fossa  is  separated  from 
the  orbit  by  the  postorbital  bar  formed  by  the  junction  of 
outgrowths  from  the  postf  rontal  and  jugal. 

3.  The   Orbits.     Each  is  bounded  behind  by  the  post- 
orbital  bar,  externally  by  the  jugal  forming  a  continuation  of 
the  infratemporal  arcade,  in  front  by  the  lachrymal,  and  inter- 
nally by  the  frontal  and  prefrontal. 

4.  The  Anterior  nares.     These  form  an  unpaired  open- 
ing bounded  by  the  prem axillae. 

Posterior  surface. 

5.  The  Foramen  magnum.     The  exoccipitals  form  the 
chief  part  of  its  boundary,  but  part  of  the  ventral  boundary 
is  formed  by  the  basi-occipital. 

6.  The  Pterygoid  fossae.     These  form  a  pair  of  large 
cavities  at  the  sides  of  the  occipital  region  of  the  skull.     The 
dorsal  boundary  is  formed  by  the  quadrate  and  quadratojugal, 
the  ventral  by  the  pterygoid,  the  internal  chiefly  by  the  quad- 
rate, pterygoid,  alisphenoid,  and  basisphenoid.     The  trarispala- 
tine  forms  a  small  part  of  the  external  boundary  which  is  in- 
complete. 

Ventral  surface. 

7.  The  Posterior  nares.    These  form  a  median  unpaired 
opening  (fig.  43,  A,  5)  bounded  by  the  pterygoids. 

8.  The     Posterior    palatine    vacuities.       Each     is 
bounded  by  the  maxilla  in  front,  the  maxilla  and  transpalatine 

R.  17 


258          THE  VERTEBRATE  SKELETON. 

externally,  the  transpalatine  and  pterygoid  behind,   and  the 
palatine  on  the  inner  side  (fig.  43,  A,  7). 

9.  The  Anterior  palatine  vacuity.  This  is  unpaired 
and  is  bounded  by  the  premaxillae  (fig.  43,  A,  8). 

(b)     THE  LOWER  JAW  OR  MANDIBLE. 

The  mandible  is  a  strong  compact  bony  structure  formed 
of  two  halves  or  rami,  which  are  suturally  united  at  the 
symphysis  in  the  middle  line  in  front.  Each  rainus  is  formed 
of  six  separate  bones. 

The  most  anterior  and  largest  of  these  is  the  dentary  (figs. 
44,  20,  and  45,  18),  which  forms  the  symphysis,  and  greater  part 
of  the  anterior  half  of  the  jaw,  and  bears  along  the  outer  part 
of  its  dorsal  border  a  number  of  sockets  or  alveoli  in  which 
the  teeth  are  placed.  Lying  along  the  inner  side  of  the  dentary 
is  a  large  splint-like  bone,  the  splenial  (fig.  45,  19),  which  does 
not  extend  so  far  forwards  as  the  symphysis,  and  is  separated 
from  the  dentary  posteriorly  by  a  large  cavity.  Forming  the 
lower  part  of  all  the  posterior  half  of  the  jaw  is  the  large 
angular  (figs.  44,  22,  and  45,  20),  which  underlies  the  posterior 
part  of  the  dentary  in  front  and  sends  a  long  process  below  that 
bone  to  the  splenial.  On  the  inner  side  of  the  jaw  there  is  an 
oval  vacuity,  the  internal  mandibular  foramen  (fig.  45,  28), 
between  the  angular  and  the  splenial ;  through  this  pass  blood- 
vessels and  branches  of  the  inferior  dental  nerve.  Lying 
dorsal  to  the  angular  is  another  large  bone,  the  supra-angular 
(figs.  44,  18,  and  45,  21).  It  extends  back  as  far  as  the  pos- 
terior end  of  the  jaw  and  forwards  for  some  distance  dorsal 
to  the  dentary  and  splenial.  It  forms  part  of  the  posterior 
margin  of  a  large  vacuity,  the  external  mandibular  foramen, 
which  is  bordered  above  and  in  front  by  the  dentary  and  below 
by  the  angular ;  it  gives  passage  to  the  cutaneous  branch  of 
the  inferior  dental  nerve.  The  concave  surface  for  articulation 
with  the  mandible  and  much  of  the  posterior  end  of  the  jaw  is 
formed  by  a  short  but  solid  bone,  the  articular  (fig.  45,  22), 


SKELETON  OF  THE  CROCODILE.   THE  HYOID.   259 

which  in  young  skulls  rather  readily  becomes  detached.  The 
remaining  mandibular  bone  is  the  coronoid  (fig.  45,  23),  a  very 
small  bone  of  irregular  shape  attached  to  the  angular  below, 
and  to  the  supra-angular  and  splenial  above. 

(c)    THE  HYOID. 

The  hyoid  of  the  Crocodile  consists  of  a  wide  flattened 
plate  of  cartilage,  the  basilingual  plate  or  body  of  the 
hyoid,  and  a  pair  of  cornua. 

The  basilingual  plate  (fig.  53,  1)  is  rounded  anteriorly 
and  marked  by  a  deep  notch  posteriorly.  The  cornua  (fig. 
53,  3),  which  are  attached  at  a  pair  of  notches  near  the  middle 
of  the  outer  border  of  the  basilingual  plate,  are  partly  ossified, 
but  their  expanded  ends  are  formed  of  cartilage.  They  pass 
at  first  backwards  and  then  upwards  and  inwards.  They 
are  homologous  with  part  of  the  first  branchial  arches  of 
Selachians. 

The  columella  and  extra-columella  have  been  already  de- 
scribed (p.  251). 

C.     THE  RIBS  AND  STERNUM. 

Thoracic  ribs. 

The  Crocodile  has  ten  pairs  of  thoracic  ribs,  all  except 
the  last  one  or  two  of  which  consist  of  three  parts, — a  verte- 
bral rib,  an  intermediate  rib  and  a  sternal  rib. 

Of  the  vertebral  ribs  the  third  may  be  taken  as  a  type, 
it  consists  of  a  curved  bony  rod  which  articulates  proximal!}7 
with  the  transverse  process  of  the  vertebra  by  two  facets. 
The  terminal  one  of  these,  the  capitulum  or  head,  articulates 
with  a  notch  on  the  side  of  the  transverse  process;  the  other, 
the  tuberculum,  which  lies  on  the  dorsal  surface  a  short 
distance  behind  the  head,  articulates  with  the  end  of  the  trans- 
verse process.  From  near  the  distal  end  an  imperfectly  ossified 
uncinate  process  (see  p.  190)  projects  backwards. 

The  intermediate  ribs  are  short  and  imperfectly  ossified  ; 
they  are  united  with  the  sternal  ribs  (fig.  46, 3),  which  are  large, 

17—2 


260          THE  VERTEBRATE  SKELETON. 

flattened,  likewise  imperfectly  ossified  structures,  and  articu- 
late at  their  distal  ends  with  a  pair  of  long  divergent  xiphi- 
sternal  horns  (fig.  46,  5),  which  arise  from  the  posterior  end 
of  the  sternum  proper.  The  last  pair  of  sternal  ribs  are  at- 
tached to  the  preceding  pair,  not  to  the  xiphisternal  horns. 

The  first  and  second  vertebral  ribs  differ  from  the  others  in 
the  fact  that  the  tuberculum  forms  a  fairly  long  outstanding 
process. 

Cervical  ribs. 

Movable  ribs  are  attached  to  all  the  cervical  as  well  as  to  the 
thoracic  vertebrae.  Those  borne  by  the  atlas  and  axis  are  long, 
narrow  structures  attached  by  a  fairly  broad  base,  and  tapering 
gradually.  The  ribs  borne  by  the  third  to  seventh  cervical 
vertebrae  are  shaped  like  a  T  with  a  double  base,  one  limb  of 
which,  corresponding  to  the  tuberculum  (fig.  41,  7),  articulates 
with  a  short  transverse  process  arising  from  the  neural  arch, 
while  the  other,  corresponding  to  the  capitulum,  articulates  with 
a  surface  on  the  centrum.  The  ribs  attached  to  the  eighth  and 
ninth  cervical  vertebrae  are  intermediate  in  character  between 
the  T-shaped  ribs  and  the  ordinary  thoracic  ribs.  The  anterior 
limb  of  the  T  is  shortened,  the  posterior  one  is  drawn  out, 
forming  the  shaft  of  the  rib.  The  distal  portion  of  the  rib  of 
the  ninth  cervical  vertebra  is  unossified. 

The  Sacral  ribs  have  been  described  in  connection  with 
the  sacral  vertebrae. 

THE  STERNUM. 

The  sternum  of  Crocodiles  is  a  very  simple  structure,  con- 
sisting of  a  plate  of  cartilage  (fig.  46,  2)  lying  immediately 
dorsal  to  the  interclavicle,  and  drawn  out  posteriorly  into  a 
pair  of  long  xiphisternal  horns  (fig.  46,  5). 

THE   ABDOMINAL    SPLINT   RIBS. 

Lying  superficially  to  the  recti  muscles  of  the  ventral  body- 
wall,  behind  the  sternal  ribs,  are  seven  or  eight  series  of 


SKELETON    OF   THE    CROCODILE.      THE   STERNUM.      261 


-2 


5 

.-3 


FIG.  46.     STERNUM  AND  ASSOCIATED   MEMBRANE  BONES  OF  A  CROCODILE 
(C.  palustris)  x  $.     (Brit.  Mus.) 

The  last  pair  of  abdominal  ribs  which  are  united  with  the  epipubes  by 
a  plate  of  cartilage  have  been  omitted. 

1.  interclavicle.  4.     abdominal  splint  rib. 

2.  sternum.  5.     xiphisternal  horn. 

3.  sternal  rib. 


262          THE  VERTEBRATE  SKELETON. 

slender  curved  bones,  the  abdominal  ribs  (fig.  46,  4).  Each 
series  consists  of  four  or  more  bones,  arranged  in  a  V-like 
form  with  the  angle  of  the  V  directed  forwards.  They  show  a 
considerable  amount  of  variability  in  number  and  character. 
They  are  really  membrane  bones,  and  are  in  no  way  homolo- 
gous with  true  ribs,  but  correspond  rather  with  the  more 
posterior  of  the  bones  constituting  the  plastron  of  Chelonia. 

2.     THE  APPENDICULAE  SKELETON. 

This  includes  the  skeleton  of  the  two  pairs  of  limbs  and 
their  respective  girdles. 


FIG.  47.     LEFT  HALF  OF  THE  PECTORAL  GIBDLE  OF  AN  ALLIGATOB  (Caiman 
latirostris)  x  f .     (Brit.  Mus. ) 

1.  scapula.  3.     interclavicle. 

2.  coracoid.  4.     glenoid  cavity. 

THE  PECTORAL  GIRDLE. 

The  pectoral  girdle  of  the  Crocodile  is  less  complete  than  is 
that   of   most    reptiles.      It   consists   of   a   dorsal   bone,   the 


SKELETON  OF  THE  CROCODILE.   PECTORAL  GIRDLE.  263 

scapula,  and  a  ventral  bone,  the  coracoid,  with  a  median 
unpaired  element,  the  interclavicle ;  but  there  is  no  separate 
representative  either  of  the  clavicle  or  precoracoid. 

The  scapula  (fig.  47,  1)  is  a  large  bone,  flattened  and  ex- 
panded above  where  it  is  terminated  by  an  unossified  margin 
the  suprascapula,  and  thickened  below  where  it  meets  the 
coracoid.  The  scapula  forms  about  half  the  glenoid  cavity 
(fig.  47,  4)  for  articulation  with  the  humerus,  and  has  the 
lower  part  of  its  anterior  border  drawn  out  into  a  roughened 
ridge. 

The  coracoid  (fig.  47,  2)  is  a  flattened  bone,  much  ex- 
panded at  either  end ;  it  bears  on  its  upper  posterior  -border  a 
flattened  surface  which  forms  half  the  glenoid  cavity,  and  is 
firmly  united  to  the  scapula  at  its  dorsal  end.  Its  ventral  end 
meets  the  sternum. 

The  interclavicle  (figs.  46,  1,  and  47,  3)  is  a  long  narrow 
blade-shaped  bone  lying  along  the  ventral  side  of  the  sternum ; 
about  a  third  of  its  length  projects  beyond  the  sternum  in 
front. 

THE  ANTERIOR  LIMB. 

This  is  as  usual  divisible  into  three  portions,  the  upper 
arm,  fore-arm  and  manus. 

The  upper  arm  or  brachium  contains  one  bone,  the 
humerus. 

The  humerus  (fig.  48,  A,  1)  is  a  fairly  long  stout  bone, 
considerably  expanded  at  either  end.  The  proximal  end  or  head 
is  evenly  rounded  and  is  formed  by  an  epiphysis  ossifying  from 
a  centre  different  from  that  forming  the  shaft.  It  articulates 
with  the  glenoid  cavity.  The  shaft  bears  on  the  flexor  surface, 
at  some  little  distance  behind  the  head,  a  prominent  rounded 
protuberance,  the  deltoid  ridge.  The  distal  end  or  trochlea 
is  also  formed  by  an  epiphysis  and  is  partially  divided  by  a 
groove  into  two  convex  surfaces ;  it  articulates  with  the  two 
bones  of  the  fore-arm,  the  radius  and  ulna. 


264 


THE  VERTEBRATE  SKELETON. 


FIG.  48. 


-20 


A,   BIGHT   ANTERIOR,    AND    B,  BIGHT   POSTERIOR    LIMB    OF    A   YOUNG 

ALLIGATOR  (Caiman  latirostris).     (Brit.  Mus.) 
A  x  4.  B  x  about  i. 


1.  humerus.  10. 

2.  radius. 

3.  ulna.  11. 

4.  radiale.  12. 

5.  ulnare.  13. 

6.  pisiform.  14. 

7.  patch  of  cartilage  representing  15. 

carpalia  1  and  2;  between 

it  and  the  radiale  should  be  16. 

another  flattened  patch,  the  17. 

centrale.  18. 

8.  carpalia  3,  4,  and  5  (fused).  19. 

9.  first  metacarpal.  20. 

21. 


proximal  phalanx  of  second 
digit. 

second  phalanx  of  fifth  digit. 

femur. 

tibia. 

fibula. 

tibiale,  intermedium  and  cen- 
trale (fused). 

fibulare. 

tarsalia  1,  2,  and  3  (fused). 

tarsalia  4  and  5  (fused). 

first  metatarsal. 

ungual  phalanx  of  second  digit. 

fifth  metatarsal. 


SKELETON    OF   THE   CROCODILE.      THE   MANUS.        265 

The  radius  and  ulna  are  nearly  equal  in  size  and  each 
consists  of  a  long  shaft  terminated  at  either  end  by  an  epi- 
physis. 

The  radius  (fig.  48,  A,  2)  or  pre-axial  bone  is  slightly  the 
smaller  of  the  two.  It  has  a  straight  cylindrical  shaft  and  is 
slightly  and  nearly  evenly  expanded  at  either  end.  The  proxi- 
mal end  which  articulates  with  the  humerus  is  flat  or  slightly 
concave,  the  distal  end  which  articulates  with  the  carpus  is 
slightly  convex. 

The  ulna  (fig.  48,  A,  3)  or  postaxial  bone  is  a  curved  bone 
rather  larger  than  the  radius.  Its  proximal  end  is  large  and 
convex,  but  is  not  drawn  out  into  an  olecranon  process. 

The  Manus  consists  of  the  carpus  or  wrist,  and  the 
hand. 

The  Carpus.  This  differs  considerably  from  the  more 
primitive  type  met  with  in  the  Turtle.  It  consists  of  six 
elements  arranged  in  a  proximal  row  of  three  and  a  distal  row 
of  two,  with  one  intervening.  The  bones  of  the  proximal  row 
are  the  radiale,  the  ulnare,  and  the  pisiform.  The  radiale 
(fig.  48,  A,  4)  is  the  largest  bone  of  the  carpus :  it  is  a  some- 
what hour-glass  shaped  bone,  with  its  ends  formed  by  flattened 
epiphyses.  It  articulates  by  its  proximal  end  with  the  whole 
of  the  radius,  and  partly  also  with  the  ulna,  and  by  its 
distal  end  with  the  centrale. 

The  ulnare  (fig.  48,  A,  5)  is  a  smaller  bone,  also  some- 
what hour-glass  shaped ;  it  articulates  proximally  with  the 
pisiform  and  radiale,  not  quite  reaching  the  ulna.  The  third 
bone  of  the  proximal  row  is  the  pisiform  (fig.  48,  A,  6),  an 
irregular  bone,  articulating  with  the  ulna,  radiale,  and  fifth 
metacarpal.  The  centrale  is  a  flattened  cartilaginous  element 
applied  to  the  distal  surface  of  the  radiale. 

The  distal  row  of  carpals  consists  of  two  small  structures. 
The  first  of  these  forms  a  small  cartilaginous  patch,  which  is 
wedged  in  between  the  first  and  second  metacarpals,  the 


266          THE  VERTEBRATE  SKELETON. 

centrale  and  the  bone  representing  carpalia  3,  4  and  5 ;  this 
cartilaginous  patch  represents  carpalia  1  and  2  (fig.  48,  A,  7). 
The  bone  representing  carpalia  3,  4  and  5  is  a  good  deal 
larger,  rounded,  and  well -ossified  ;  it  articulates  with  the 
ulnare,  the  pisiform,  and  the  third,  fourth,  and  fifth  meta- 
carpals. 

The  hand.  Each  of  the  five  digits  consists  of  an  elongated 
metacarpal,  terminated  at  each  end  by  an  epiphysis,  and  of  a 
varying  number  of  phalanges.  The  terminal  phalanx  of  each 
digit  has  an  epiphysis  only  at  its  proximal  end,  the  others  have 
them  at  both  ends. 

The  first  digit,  or  pollex,  is  the  stoutest,  and  has  two 
phalanges,  the  second  has  three,  the  third  four,  the  fourth 
three,  and  the  fifth  two.  The  terminal  phalanx  of  each  of  the 
first  three  digits  is  pointed  and  sheathed  in  a  horny  claw ;  and 
is  also  marked  by  a  pair  of  prominent  lateral  grooves. 

THE  PELVIC  GIRDLE. 

The  pelvic  girdle  of  the  Crocodile  consists  of  four  parts,  a 
dorsal  element,  the  ilium,  an  anterior  ventral  element,  the 
pubis,  a  posterior  ventral  element,  the  ischium,  and  an 
accessory  anterior  ventral  element,  the  epipubis.  All  except 
the  epipubis  take  part  in  the  formation  of  the  acetabulum, 
which  is  perforated  by  a  prominent  hole. 

The  ilium  (fig.  49,  1)  is  a  thick  strong  bone,  firmly  united 
on  its  inner  side  with  the  two  sacral  ribs.  Its  dorsal  border 
is  rounded,  its  ventral  border  bears  posteriorly  two  irregular 
surfaces,  completed  by  epiphyses,  which  are  united  respectively 
with  the  ischium  and  pubis. 

The  ischium  (fig.  49,  2)— the  largest  bone  of  the  pelvis, 
is  somewhat  contracted  in  the  middle  and  expanded  at  either 
end.  Its  proximal  end,  which  is  formed  by  an  epiphysis, 
bears  two  surfaces,  one  of  which  is  united  to  the  ilium, 
while  the  other  forms  part  of  the  acetabulum.  The  anterior 
border  is  also  drawn  out  dorsally  into  a  strong  process,  which 


SKELETON    OF   THE   CROCODILE.      PELVIC   GIRDLE.     26*7 

is  terminated  by  a  convex  epiphysis,  and  is  united  to  the 
pubis.  The  ventral  end  of  the  ischium  forms  a  flattened  blade, 
meeting  its  fellow  in  a  median  symphysis. 

The  pubis  (fig.  49,  3)  is  much  smaller  than  either  the  ilium 
or  ischium ;  it  forms  a  small  patch  of  unossified  cartilage,  in- 
terposed between  the  anterior  parts  of  the  ilium  and  ischium. 


FIG.  49.     PELVIS  AND  SACBUM  OF  AN  ALLIGATOR  (Caiman  latirostris)  x 
(Brit.  Mus.) 


1.  ilium. 

2.  ischium. 

3.  true  pubis. 

4.  epipubis  (so-called  pubis). 

5.  acetabular  foramen. 


6.  neural  spines  of  sacral  verte- 

brae. 

7.  symphysis  ischii. 

8.  process    bearing  prezygapo- 

physis. 


The  epipubis  (fig.  49,  4)  is  a  large  bone  with  a  thickened 
proximal  end,  which  is  loosely  articulated  to  the  ischium,  and 
a  flattened  expanded  distal  end,  which  is  united  with  its  fellow, 
and  with  the  last  pair  of  abdominal  ribs  by  a  large  plate  of 
cartilage.  This  bone  is  generally  described  as  the  pubis. 


268          THE  VERTEBRATE  SKELETON. 

THE  POSTERIOR  LIMB. 

This  is  as  usual  divisible  into  three  portions,  the  thigh, 
the  crus  or  shin,  and  the  pes. 

The  thigh  is  formed  by  the  femur  (fig.  48,  B,  12),  a 
moderately  long  stout  bone,  not  unlike  the  humerus  ;  it  arti- 
culates with  the  acetabulum  by  a  fairly  prominent  rounded 
head.  The  distal  end  articulating  with  the  tibia  and  fibula 
is  also  expanded,  and  is  partially  divided  into  equal  parts  by 
anterior  and  posterior  grooves.  The  flexor  surface  bears  a 
fairly  prominent  trochanteric  ridge.  Each  end  of  the  femur 
is  formed  by  an  epiphysis. 

The  cms  or  shin  includes  two  bones,  the  tibia  and 
fibula.  Both  are  well  developed,  but  the  tibia  is  considerably 
the  larger  of  the  two. 

The  tibia  (fig.  48,  B,  13)  is  a  strong  bone  with  a  flattened 
expanded  proximal  end  articulating  with  almost  the  whole  of 
the  end  of  the  femur,  and  a  similarly  expanded  distal  end 
articulating  with  a  bone  representing  the  fused  astragalus  and 
centrale. 

The  fibula  (fig.  48,  B,  14)  is  flattened  proximally,  and 
articulates  with  only  quite  a  small  part  of  the  femur,  while 
distally  it  is  more  expanded,  and  articulates  with  the  fibulare 
(calcaneum)  and  with  a  facet  on  the  side  of  the  fused  astra- 
galus and  centrale. 

The  Pes  consists  of  the  tarsus  or  ankle,  and  the  foot. 

The  Tarsus.  This,  like  the  carpus,  is  much  reduced  and 
modified  from  the  primitive  condition.  It  consists  of  only 
four  bones,  arranged  in  two  rows  of  two  each.  The  two 
bones  of  the  proximal  row  are  much  larger  than  are  those  of 
the  distal  row.  The  pre-axial  of  them  (fig.  48,  B,  15)  repre- 
senting the  fused  astragalus  (tibiale  and  intermedium)  and 
centrale,  articulates  proximally  with  the  tibia  and  fibula,  and 
distally  with  the  first  metatarsal,  and  a  small  bone  representing 
the  first  three  tarsalia.  The  post-axial  bone,  the  calcaneum 


SKELETON  OF  THE  CROCODILE.   THE  PES.      269 

(fibulare)  (fig.  48,  B,  1 6),  is  drawn  out  into  a  prominent  posterior 
process  forming  a  heel  such  as  is  almost  unknown  elsewhere 
except  in  mammals.  It  articulates  with  the  fibula,  the  tibiale- 
centrale,  and  distally  with  a  bone  representing  the  fourth  and 
fifth  tarsalia,  and  with  the  fifth  metatarsal. 

The  two  bones  forming  the  distal  row  of  tarsals  are  both 
small  and  rounded ;  one  represents  the  first  three  tarsalia  fused 
together,  the  other  tarsalia  4  and  5. 

The  Foot.  The  foot  has  five  digits,  but  the  fifth  is  much 
reduced,  consisting  only  of  a  short  metatarsal.  The  first  four 
metatarsals  are  all  long  bones,  slightly  expanded  at  each 
end,  and  terminated  by  small  epiphyses.  The  first  digit  has 
two  phalanges,  the  second  three,  the  third  four,  and  the  fourth 
five.  The  terminal  or  ungual  phalanx  in  each  instance  is 
grooved  and  pointed,  and  in  the  case  of  the  first  three  digits 
bears  a  horny  claw.  The  ungual  phalanx  progressively  de- 
creases in  size  from  the  first  to  the  fourth.  The  fifth  digit 
consists  only  of  a  small,  somewhat  square  metatarsal  (fig.  48, 
B,  21),  attached  to  the  bone  representing  the  fused  fourth  and 
fifth  tarsalia. 


CHAPTER   XVI. 

GENERAL   ACCOUNT   OF   THE   SKELETON   IN 
REPTILES. 

EXOSKELETON. 

The  exoskeleton  both  epidermal  and  dermal  is  exceedingly 
well  developed  in  reptiles. 

EPIDERMAL  EXOSKELETON. 

This  generally  has  the  form  of  overlapping  horny  scales 
which  invest  outgrowths  of  the  dermis,  and  are  found  covering 
the  whole  body  in  most  Rhynchocephalia,  Ophidia,  and  Lacer- 
tilia,  and  many  Crocodilia.  In  the  Ophidia  the  ventral  surface 
of  the  tail  is  commonly  covered  by  a  double  row  of  broad  scales, 
while  the  ventral  surface  of  the  precaudal  part  of  the  body  is 
covered  by  a  single  row.  In  the  burrowing  snakes  (Typhlo- 
pidae)  and  some  sea  snakes  (Hydrophidae)  these  broad  scales 
do  not  occur,  the  scales  of  the  ventral  surface  being  similar  to 
those  of  the  dorsal. 

In  the  Chelonia  with  the  exception  of  Dermochelys,  Trionyx 
and  their  allies  there  is  a  well-developed  system  of  horny  shields 
having  a  regular  arrangement  which  has  been  described  in  the 
account  of  the  Turtle's  skeleton1. 

The  rattle  of  the  rattlesnake  is  an  epidermal  structure 
formed  of  several  loosely  articulated  horny  rings,  produced  by 
the  modification  of  the  epidermal  covering  of  the  end  of  the 
tail,  which  instead  of  being  cast  off  when  the  rest  of  the  outer 
skin  is  shed  is  retained  loosely  interlocked  with  the  adjoining 

1  See  pp.  214  and  215. 


THE    SKELETON    IN    REPTILES.     EXOSKELETON.        271 

ring  or  joint.  New  rings  are  thus  periodically  added  to  the 
base  of  the  rattle,  and  in  old  animals  the  terminal  ones  wear 
away  and  are  lost. 

Horny  claws  occur  on  the  ends  of  some  or  all  of  the  digits 
in  most  living  reptiles. 

Owen's  Chameleon  bears  three  epidermal  horns,  one  arising 
from  the  nasal  and  two  from  the  frontal  region. 

In  the  Chelonia,  some  of  the  Theromorpha  such  as  Ude- 
nodon  and  Dicynodon,  probably  also  in  the  Pterosauria  and 
Polyonax  among  the  Dinosaurs,  the  jaws  are  more  or  less 
cased  in  horny  beaks.  The  horny  beaks  of  Chelonia  are 
variable ;  sometimes  they  have  cutting  edges,  sometimes  they 
are  denticulated,  sometimes  they  are  adapted  for  crushing. 

DERMAL  EXOSKELETON. 

Nearly  all  Crocodilia,  many  Dinosauria,  some  Rhynchoce- 
phalia  and  Pythonomorpha,  and  some  Lacertilia  such  as  Tiliqua, 
Scincus  and  Anguis  have  a  dermal  exoskeleton  of  bony  scutes, 
developed  below  and  corresponding  in  shape  to  the  epidermal 
scales.  Sometimes  as  in  Caiman  sclerops,  Jacare  and  Teleo- 
saurus,  the  scutes  completely  invest  the  body,  being  so 
arranged  as  to  form  a  dorsal  and  a  ventral  shield,  and  a  con- 
tinuous series  of  rings  round  the  tail.  In  Crocodilus  they  are 
confined  to  the  dorsal  surface,  and  in  Alligator  to  the  dorsal 
and  ventral  surfaces.  The  scutes  of  some  extinct  forms  articu- 
late with  one  another  by  a  peg  and  socket  arrangement  as  in 
some  Ganoid  fish. 

The  carapace  of  most  Chelonia  is  a  compound  structure, 
being  partly  endoskeletal  and  formed  from  the  ribs  and  verte- 
brae, partly  from  plates  derived  from  the  dermal  exoskeleton. 
The  common  arrangement  is  seen  in  fig.  36.  All  the  surface 
plates  are  probably  exoskeletal  in  origin,  but  united  with  the 
ventral  surfaces  of  the  costal  and  neural  plates  respectively  are 
the  expanded  ribs  and  neural  arches  of  the  vertebrae. 

The   plastron  in   the   common   genus    Chelone    (fig.   37) 


272          THE  VERTEBRATE  SKELETON. 

includes  nine  plates  of  bone,  one  unpaired  and  four  pairs ; 
they  will  be  referred  to  in  connection  with  the  ribs  and  pec- 
toral girdle. 

In  the  Leathery  Turtle  (Dermochelys)  the  carapace  and 
plastron  differ  completely  from  those  of  any  other  living 
form.  The  carapace  consists  of  a  number  of  polygonal  ossifi- 
cations fitting  closely  togethei  and  altogether  distinct  from  the 
vertebrae  and  ribs.  The  plastron  is  imperfectly  ossified,  and 
not  united  with  the  pelvis,  and  the  whole  surface  of  both 
carapace  and  plastron  is  covered  with  a  tough  leathery  skin, 
without  horny  shields. 

Some  of  the  extinct  Dinosauria  have  an  enormously  de- 
veloped dermal  exoskeleton.  Thus  in  Stegosaurus  and  Omo- 
saurus  the  dorsal  surface  is  provided  with  flattened  plates  or 
with  spines  reaching  a  length  of  upwards  of  two  feet.  In 
Polacanthus  the  posterior  part  of  the  body  is  protected  by  a 
bony  shield  somewhat  recalling  that  of  the  little  armadillo 
Chlamydophorus.  No  exoskeleton  is  known  in  Ichthyosauria, 
Sauropterygia,  Pterosauria,  many  Dinosauria  and  Theromorpha, 
and  some  Lacertilia,  such  as  Chamadeon  and  Amphisbaena. 

TEETH. 

The  teeth  of  reptiles  are  generally  well  developed,  and  in 
the  great  majority  of  forms  are  simple  conical  structures, 
uniform  in  character,  generally  somewhat  recurved,  and  often 
with  serrated  edges.  Another  common  type  of  tooth  is  that 
with  a  laterally  compressed  triangular  crown  provided  with 
a  double  cutting  edge  which  may  or  may  not  be  serrated.  The 
teeth  are  mainly  formed  of  dentine,  with  usually  an  external 
layer  of  enamel,  and  often  a  coating  of  cement  on  the  root. 
Vasodentine  is  found  below  the  dentine  in  Iguanodon.  The 
teeth  of  reptiles  never  have  the  enamel  deeply  infolded,  nor 
do  they  have  double  roots. 

Teeth  may  be  present  not  only  on  the  jaw-bones,  but  as  in 
many  Squamata,  also  on  the  palatines,  pterygoids  or  vomers. 


THE   SKELETON    IN    REPTILES.      THE   TEETH.          273 

The  method  by  which  they  are  attached  to  the  bones  varies 
much.  Sometimes  as  in  Iguana  and  some  other  lizards,  they 
are  pleurodont1,  sometimes  they  are  acrodont1,  as  in  the  Rhyn- 
chocephalia,  Pythonomorpha,  Ophidia  and  some  Lacertilia  such 
as  Agama.  Again  they  may  be  set  in  a  continuous  groove 
as  in  the  Ichthyosauria  and  young  Crocodilia.  Finally  the 
teeth  may  be  thecodont  or  placed  in  distinct  sockets  as  in  the 
Theromorpha,  Sauropterygia,  adult  Crocodilia,  Sauropoda  and 
Theropoda.  In  Iguanodon  the  teeth  are  set  in  shallow  sockets 
in  a  groove  one  side  of  which  is  higher  than  the  other ;  the 
method  of  attachment  thus  shows  points  of  resemblance  to 
the  thecodont  condition,  the  pleurodont  condition,  and  that 
met  with  in  the  Ichthyosauria. 

In  Ichthyosaurus  the  teeth  are  marked  by  a  number  of 
vertical  furrows,  and  it  is  from  a  furrow  of  this  nature  greatly 
enlarged  and  converted  into  a  tube  that  the  channel  down 
which  flows  the  poison  of  venomous  snakes  is  derived. 

In  most  reptiles  the  dentition  is  more  or  less  homodont. 
The  only  reptiles  in  which  a  definite  heterodont  dentition  is 
known  are  the  extinct  Theromorpha,  and  in  them  the  teeth 
vary  greatly.  Thus  Udenodon  is  toothless,  the  jaws  having 
been  probably  cased  in  a  horny  beak.  In  Dicynodon  the  jaws 
are  likewise  toothless  with  the  exception  of  a  pair  of  perma- 
nently growing  tusks  borne  by  the  maxillae.  Dicynodon  is  the 
only  known  reptile  whose  teeth  have  permanently  growing 
pulps.  In  Pariasaurus  the  teeth  are  uniform  and  very  nume- 
rous, and  though  placed  in  distinct  sockets  are  ankylosed  to 
the  jaw.  In  Galesaurus  and  Cynognathus  three  kinds  of  teeth 
can  be  distinguished,  slender  conical  incisor-like  teeth,  large 
canine -like  teeth,  and  cheek  teeth  with  two  or  three  cusps. 
The  teeth  in  Galesaurus  are  confined  to  the  jaws,  in  Placodus 
and  its  allies,  however,  large  flat  crushing  teeth  are  attached  to 
the  palatines  as  well  as  to  the  jaw-bones,  and  in  Pariasaurus 
the  vomer,  palatine  and  pterygoid  all  bear  teeth  as  well  as  the 

1  These  terms  are  defined  on  p.  199. 
B.  18 


274 


THE  VERTEBRATE  SKELETON. 


jaw  bones.  The  upper  jaw  of  Sphenodon  and  other  Rhyn- 
chocephalia  is  provided  with  two  parallel  rows  of  teeth,  one 
borne  on  the  maxillae  and  one  on  the  palatines,  the  man- 
dibular  teeth  bite  in  a  groove  between  these  two  rows.  The 
bone  of  the  jaws  in  Sphenodon  is  so  hard  that  when  the  teeth 
get  worn  away,  it  can  act  as  a  substitute.  In  the  young 
Sphenodon  the  vomers  bear  teeth,  as  they  do  also  in  Protero- 
saurus, 

There  is  generally  a  continuous  succession  of  teeth  through- 
out life,  the  new  tooth  coming  up  below,  or  partly  at  the  side 
of  the  one  in  use,  and  causing  the  absorption  of  part  of  its 
wall  or  base.  In  this  way  the  new  tooth  conies  to  lie  in  the 
pulp  cavity  of  the  old  one.  This  method  of  succession  is  well 
seen  in  the  Crocodilia. 


FIG.    50.     PBEPABATION   OP  PART   OF   THE   BIGHT   MANDIBULAB  BAMUS  or 
Crocodilus  palustris  x  \.     (Brit.  Mus.) 


1.  tooth  in  use. 

2.  fairly    old    germ    of    future 

tooth. 


3.     symphysial    surface   of   the 
mandible. 


Teeth  have  been  detected  in  embryos  of  Trionyx,  but 
otherwise  no  teeth  are  known  to  occur  in  Chelonia,  or  in 
Pteranodon  (Pterosauria),  while  the  anterior  part  of  the  jaw 
is  edentulous  in  Iguanodon,  Polyonax  and  some  other  Dino- 
saurs, and  in  Rliamphorhynchus. 


THE   SKELETON   IN   REPTILES.      VERTEBRAL   COLUMN.    275 

ENDOSKELETON. 

VERTEBRAL  COLUMN. 

The  vertebral  column  is  commonly  divisible  into  the  usual 
five  regions,  but  in  the  Ophidia,  Ichthyosauria,  and  Amphis- 
baenidae  among  Lacertilia,  only  into  caudal  and  precaudal 
regions.  In  the  Chelonia  there  are  no  lumbar  vertebrae. 

The  form  of  the  vertebral  centra  is  very  variable.  A  large 
proportion  of  extinct  reptiles, — several  entire  orders, — and  the 
earlier  and  more  primitive  forms  in  some  of  the  other  groups 
have  amphicoelous  vertebrae.  Vertebrae  of  this  type  occur 
in  the  Theromorpha,  Ichthyosauria,  most  Sauropterygia  and 
Rhynchocephalia,' and  many  Dinosauria,  also  in  some  of  the 
early  Crocodilia  such  as  Belodon,  Teleosaurus  and  Goniopholis, 
and  the  Geckonidae  among  Lacertilia. 

The  majority  of  living  reptiles  have  procoelous  vertebrae. 
Thus  they  occur  in  the  Lacertilia  (excluding  the  Geckos),  the 
Ophidia,  and  the  Crocodilia,  also  among  extinct  forms  in  the 
Pterosauria  and  many  Dinosauria.  On  the  other  hand  some 
Dinosauria  such  as  Iguanodon  have  opisthocoelous  cervical 
vertebrae,  while  others  have  opisthocoelous  thoracic  vertebrae. 
The  vertebrae  of  the  Ceratopsidae  and  some  Sauropterygia, 
the  thoracic  vertebrae  of  Iguanodon,  and  the  sacral  vertebrae 
of  Crocodilia  have  flat  centra.  The  first  caudal  vertebra  of 
modern  Crocodilia  is  biconvex,  and  in  the  Chelonia  all  types 
of  vertebral  centra  are  found.  The  cervical  vertebrae  of 
Sphenodon  are  noticeable  for  the  occurrence  of  a  small  pro- 
atlas,  which  may  represent  the  neural  arch  of  a  vertebra  in 
front  of  the  atlas. 

In  most  reptiles  the  vertebrae  are  fully  ossified,  but  in 
some  of  the  more  primitive  forms  the  notochord  persists  in 
the  centre  of  the  vertebra  (i.e.  intervertebrally),  this  is  the 
case  for  instance  in  many  of  the  Theromorpha  and  Rhyncho- 
cephalia, and  also  in  the  Geckos.  In  other  reptiles  it  persists 
longest  intravertebrally. 

The  centrum  of  each  of  the  caudal  vertebrae  of  most 

18—2 


276  THE   VERTEBKATE   SKELETON. 

Lacertilia  is  traversed  by  an  unossified  septum  along  which  it 
readily  breaks. 

Chevron  bones  occur  below  the  caudal  vertebrae  in  Lacertilia, 
Chelonia,  Ichthyosauria,  many  Dinosauria,  and  Sphenodon, 
articulating  with  quite  the  posterior  part  of  the  centrum  which 
bears  them.  In  Lacertilia  and  Orocodilia  (fig.  41,  3)  the  axis 
has  a  well-marked  odontoid  process.  The  ventral  portions  of 
the  intervertebral  discs  are  sometimes  ossified,  forming  wedge- 
shaped  intercentra,  as  in  Geckos,  and  the  cervical  vertebrae  of 
Sphenodon. 

In  snakes,  Theropod  Dinosaurs,  and  the  iguanas  among 
lizards,  the  neural  arches  are  provided  with  zygosphenes,  and 
zygantra. 

The  neural  arches  are  usually  firmly  ankylosed  to  the 
centra,  but  in  the  Crocodilia  and  some  Chelonia,  Sauropterygia, 
and  Dinosauria,  the  suture  between  the  centrum  and  neural 
arch  persists  at  any  rate  till  late  in  life.  In  the  Ichthyosauria 
the  neural  arches  were  united  to  the  centra  by  cartilage  only. 

The  thoracic  vertebrae  of  some  of  the  Theromorpha  (Dime- 
trodon)  are  remarkable  for  the  extraordinary  development  of 
the  neural  spine,  and  those  of  Chelonia  for  the  absence  of 
transverse  processes. 

In  living  reptiles  the  number  of  sacral  vertebrae  is  nearly 
always  two,  but  in  the  Theromorpha,  Dinosauria,  and  Ptero- 
sauria,  as  many  as  five  or  six  bones  may  be  ankylosed  together 
in  the  sacral  region.  In  Crocodiles  the  two  halves  of  the  pelvis 
sometimes  articulate  with  different  vertebrae.  The  vertebrae 
of  some  of  the  great  Sauropoda  are  remarkably  hollowed  out, 
having  a  large  vacuity  on  each  side  of  the  centrum  communi- 
cating with  a  series  of  internal  cavities.  The  whole  structure 
of  these  vertebrae  shows  a  combination  of  great  strength  with 
lightness. 

THE  SKULL. 

The  reptilian  skull  is  well  ossified  and  the  bones  are  noticeable 
for  their  density.  The  true  cranium  is  often  largely  concealed 


THE    SKELETON   IN    REPTILES.      THE   SKULL.  277 

by  a  secondary  or  false  roof  of  membrane  bones,  which  is  best 
seen  in  the  Ichthyosauria  and  some  of  the  Chelonia.  In  other 
reptiles  the  false  roof  is  more  or  less  broken  up  by  vacuities 
exposing  the  true  cranial  walls.  The  ethmoidal  region  is  the 
only  one  in  which  much  of  the  primordial  cartilaginous  cranium 
remains.  The  lateral  parts  of  'the  sphenoidal  region  are  also 
as  a  rule  not  well  ossified. 

In  some  reptiles,  such  as  most  Lacertilia  and  Chelonia,  the 
orbits  are  separated  only  by  the  imperfect  interorbital  septum, 
while  in  others,  such  as  the  Ophidia,  Crocodilia  and  Amphis- 
baenidae,  the  cranial  cavity  extends  forwards  between  the 
orbits. 

In  the  occipital  region  all  four  bones  are  ossified.  The 
great  majority  of  reptiles  have  a  single  convex  occipital 
coiidyle,  but  some  of  the  Theromorpha  such  as  Cynognatlius 
have  two  distinct  condyles  as  in  mammals.  Sometimes,  as 
in  Chelonia,  Ophidia  and  Lacertilia,  the  exoccipitals,  as  well 
as  the  basi-occipital,  take  part  in  the  formation  of  the  single 
condyle ;  sometimes,  as  in  Crocodiles,  it  is  formed  by  the  basi- 
occipital  alone,  as  in  birds.  The  relations  of  the  bones  to  the 
foramen  magnum  vary  considerably,  in  Chelonia  the  basi- 
occipital  generally  takes  no  part  in  bounding  it,  and  in  the 
Theromorpha,  Crocodilia,  and  Ophidia,  the  supra-occipital  is 
excluded.  The  parietals  are  paired  in  Geckos  and  Chelonia 
alone  among  living  forms,  and  in  the  extinct  Ichthyosauria 
and  some  Theromorpha ;  in  all  other  reptiles  they  are  united. 

The  frontals  are  paired  in  Ichthyosauria  (fig.  32,  5), 
Chelonia,  Ophidia,  Sphenodon  (fig.  52,  B,  4)  and  some  extinct 
crocodiles,  such  as  Belodon.  They  are  completely  fused  in 
living  Crocodilia  and  some  Lacertilia  and  Dinosauria.  In 
the  gigantic  Polyonax  they  are  drawn  out  into  a  pair  of 
enormous  horns,  and  the  parietals  and  squamosals  are  greatly 
expanded  behind. 

An  interparietal  foramen  occurs  in  the  Theromorpha,  the 
Ichthyosauria  (fig.  32,  10),  Sphenodon,  the  Sauropterygia  and 


278          THE  VERTEBRATE  SKELETON. 

most  Lacertilia.  The  posterior  part  of  the  skull  is  curiously 
modified  in  some  Chamaeleons,  the  parietal  s  and  supra- occipitals 
being  drawn  out  into  a  backwardly-projecting  sagittal  crest 
which  unites  with  the  two  prolongations  from  the  squamosals. 
In  other  Chamaeleons  (C.  bifidus)  prolongations  of  the  pre- 
frontals  and  maxillae  form  large  forwardly-projecting  bony 
processes. 

The  roof  of  the  skull  is  characterised  by  the  development 
of  prefrontals  and  postfrontals,  which  lie  respectively  near  the 
anterior  and  posterior  extremity  of  the  orbit.  In  Theromorpha, 
Squamata,  Crocodilia,  arid  some  Dinosauria  lachrymals  are 
developed.  There  is  a  ring  of  bones  in  the  sclerotic  in  the 
Ichthyosauria  (fig.  32,  15),  the  Metriorhynchidae  among  Croco- 
diles and  some  Rhynchocephalia,  Dinosauria,  and  Pterosauria. 

The  pro-otic  lies  in  front  of  the  exoccipital  and  together 
with  the  opisthotic  forms  the  hind  border  of  the  fenestra 
ovalis.  In  Chelonia  the  opisthotic  remains  separate,  in  all  other 
living  reptiles  it  fuses  with  the  exoccipital.  The  epi-otic  fuses 
with  the  supra-occipital. 

The  parasphenoid,  so  important  in  Ichthyopsids,  has  very 
often  disappeared  completely;  it  is  present,  however,  in  the* 
Ichthyosauria,  the  Plesiosauridae,  and  a  number  of  Squamata, 
in  many  Ophidia  its  anterior  part  forming  the  base   of   the 
interorbital  septum. 

In  the  Plesiosauridae  and  most  Lacertilia,  but  not  in  the 
Amphisbaenidae,  a  slender  bone,  the  epipterygoid,  occurs  unit- 
ing the  parietal  or  the  anterior  end  of  the  pro-otic  with  the 
pterygoid.  A  homologous  arrangement  occurs  in  the  Ichthyo- 
sauria and  some  Chelonia. 

In  most  reptiles  a  transpalatine  occurs,  connecting  the 
maxilla  with  the  pterygoid,  but  this  is  absent  in  the  Chelonia, 
and  some  Dinosauria,  and  in  the  Typhlopidae  among  snakes. 

The  quadrate  is  always  well  developed,  and  except  in  the 
Squamata  is  firmly  fixed  to  the  surrounding  bones.  The 
Chamaeleons  also,  among  the  Squamata,  have  a  fixed  quadrate, 


THE    SKELETON    IN    REPTILES.      THE    SKULL. 


279 


and  in  them  too  the  quadratojugal  is  absent.     Separate  nasal 
bones  do  not  occur  in  any  living  Chelonia. 

The  vomers  are  generally  paired   as  in  Squamata,   some- 
times unpaired  as  in  Chelonia. 


FIG.  51.     DOKSAL  (TO  THE  LEFT)  AND  VENTRAL  (TO  THE  RIGHT)  VIEWS  OF 
THE  SKULL  OF  THE  COMMON  SNAKE  (Tropidinotus  natrix).     (After  PARKER.) 


1.  premaxillae  (fused). 

2.  anterior  nares. 

3.  nasal. 

4.  prefrontal. 

5.  frontal. 

6.  parietal. 

7.  maxilla. 

8.  transpalatine. 

9.  palatine. 

10.  pterygoid. 

11.  pro-otic. 

12.  exoccipital. 

13.  supra-occipital. 

14.  opisthotic. 

15.  epi-otic. 


16.  quadrate. 

17.  parasphenoid. 

18.  basisphenoid. 

19.  basi-occipital. 

20.  occipital  condyle. 

21.  splenial. 

22.  dentary. 

23.  angular. 

24.  articular. 

25.  supra-angular. 

26.  coronoid. 

27.  vomer. 

28.  squamosal. 

IX,   X  foramina   for  the   ninth 

and  tenth  cranial  nerves. 


280          THE  VERTEBRATE  SKELETON. 

The  disposition  of  the  bones  of  the  jaws  is  subject  to 
much  modification  in  the  Ophidia  in  order  to  adapt  them  for 
swallowing  very  large  prey.  The  arrangements  again  differ 
greatly  in  the  venomous  and  non-venomous  snakes.  In  the 
non-venomous  snakes,  such  as  Python  and  Tropidonotus,  the 
palatine  is  large  and  is  fixed  to  the  pterygoid  which  extends 
outwards  (fig.  51,  10)  so  as  to  be  united  to  the  quadrate,  and 
is  at  the  same  time  firmly  connected  by  the  transpalatine  with 
the  maxilla.  The  quadrate  is  united  to  the  squamosal,  which 
is  loosely  attached  to  the  cranium.  The  premaxilla  is  moder- 
ately developed  and  bears  teeth,  and  the  maxilla  forms  a  long 
bar  loosely  connected  with  the  rest  of  the  skull.  The  rami  of 
the  mandible  are  united  only  by  an  extremely  elastic  ligament. 
It  is  as  regards  the  maxillae  and  premaxillae  that  the  skulls 
of  venomous  and  non-venomous  snakes  differ  most.  In  the 
rattlesnake  (Crotalus)  and  other  venomous  snakes  the  pre- 
maxilla is  extremely  small  and  toothless.  The  maxilla  is 
small  and  subcylindrical,  and  is  movably  articulated  to  the 
lachrymal,  which  also  is  capable  of  a  certain  amount  of  motion 
on  the  frontal.  The  maxilla  is  connected  by  means  of  the 
transpalatine  with  the  pterygoid,  which  in  its  turn  is  united 
to  the  quadrate.  When  the  mouth  is  shut  the  quadrate  is 
directed  backwards,  and  carrying  back  the  pterygoid  and 
transpalatine  pulls  at  the  maxilla  and  causes  its  palatal  face, 
to  which  the  poison  teeth  are  attached,  to  lie  back  along  the 
roof  of  the  mouth.  When  the  mouth  opens  the  distal  end 
of  the  quadrate  is  thrust  forward,  and  this  necessitates  the 
pushing  forward  of  the  pterygoid  and  transpalatine,  causing 
the  tooth-bearing  surface  of  the  maxilla  to  look  downwards 
and  the  tooth  to  come  into  the  position  for  striking. 

The  Ophidian  skull  is  also  noticeable  for  the  absence  of  the 
jugals  and  quadratojugals.  In  poisonous  snakes  the  place  of 
the  jugal  is  taken  by  the  zygomatic  ligament  which  connects 
the  quadrate  and  maxilla. 

The  extent  to  which  the  palate  is  closed  in  reptiles  varies 


THE   SKELETON    IN    REPTILES.      THE   SKULL.          281 

much.  In  many  reptiles,  such  as  the  Squamata  and  Ichthyo- 
sauria,  the  palate  is  not  complete,  both  palatines  and  pterygoids 
being  widely  separated  in  the  middle  line.  In  others,  such  as 
the  Crocodilia,  Sauropterygia,  and  Chelonia,  there  is  a  more 
or  less  complete  bony  palate.  In  many  Chelonia  this  is 
chiefly  formed  of  the  vomer,  palatines,  and  pterygoids,  the 
posterior  nares  being  mainly  bounded  by  the  palatines.  In 
living  Crocodilia,  however,  outgrowths  are  formed  from  the 
pterygoids  and  palatines  which  arch  round  and  meet  one 
another  vent  rally,  forming  a  secondary  palate  (fig.  43,  A), 
which  completely  shuts  off  the  true  sphenoidal  floor  of  the 
skull,  and  causes  the  posterior  nares  which  are  bounded  by 
the  pterygoids  to  open  very  far  back.  Though  this  feature 
is  common  to  all  postsecondary  crocodiles,  it  is  interesting  to 
notice  that  it  is  not  found  in  the  earlier  forms,  but  that  its 
gradual  evolution  can  be  traced.  In  the  Triassic  Belodon,  for 
instance,  the  posterior  nares  open  far  forwards,  and  are  not 
surrounded  by  either  the  palatines  or  pterygoids.  In  the 
Jurassic  crocodile,  Teleosaurus,  the  posterior  nares  lie  further 
back,  being  surrounded  by  the  palatines,  but  the  pterygoids 
do  not  meet  them.  Finally,  in  the  Tertiary  forms  the  arrange- 
ments are  as  in  living  crocodiles. 

A  short  secondary  hard  palate  is  found  also  in  the  Therio- 
dontia.  The  palatines  of  Ichthyosaurus  are  noticeable  for  their 
transverse  position,  which  recalls  that  in  the  Frog. 

The  various  fossae  or  vacuities  in  the  false  roof  of  the 
skull  are  important,  and  their  relations  may  best  be  understood 
by  a  description  of  their  mode  of  occurrence  in  Sphenodon,  a 
form  in  which  they  are  very  completely  developed. 

In  Sphenodon,  then,  on  the  dorsal  surface  of  the  skull,  are 
the  large  supratemporal  fossae  (fig.  52,  20).  Their  inner 
margins  are  separated  from  one  another  by  the  parietal  walls 
of  the  cranium,  while  externally  each  is  bounded  by  a  bony 
arch,  the  supratemporal  arcade,  formed  of  the  postfrontal, 
post-orbital,  and  squamosal.  Posteriorly  the  boundary  is 


282 


THE  VERTEBRATE  SKELETON. 


FIG.  52.     SKULL  OF  HATTEBIA    (Sphenodon  punctatus). 
A,  lateral;  B,  dorsal;  .C,  ventral;  D,  posterior.     (After  VON  ZITTEL.) 


1.  premaxilla. 

2.  nasal. 

3.  pref rental. 

4.  frontal. 

5.  postfrontal. 

6.  parietal. 

7.  squamosal. 

8.  quadratojugal. 

9.  quadrate. 

10.  postorbital. 

11.  jugal. 

12.  maxilla. 

13.  vomer. 

14.  palatine. 

15.  pterygoid. 


16.  transpalatine. 

17.  exoccipital. 

18.  epipterygoid. 

19.  basisphenoid. 

20.  supratemporal  fossa. 

21.  infratemporal  or  lateral  tem- 

poral fossa. 

22.  orbit. 

23.  post-temporal  fossa. 

24.  foramen  magnum. 

25.  anterior  nares. 

26.  interparietal  foramen. 

27.  dentary. 

28.  supra-angular. 

29.  articular. 


THE  SKELETON  IN  REPTILES.   THE  SKULL.    283 

formed  by  a  post-temporal  bar,  formed  by  the  parietal  and 
squamosal.  Below  the  supra  temporal  arcade  is  another  large 
vacuity,  the  infra-temporal  or  lateral  temporal  fossa  (fig. 
52,  21).  This  is  bounded  above  by  the  supratemporal  arcade, 
and  is  separated  from  the  orbit  in  front  by  the  postorbital 
bar,  formed  by  the  union  of  outgrowths  from  the  jugals  and 
postorbitals.  Behind  it  is  bounded  by  a  continuation  of  the 
post-temporal  bar  formed  of  the  squamosal  and  quadratojugal, 
and  below  by  an  infratemporal  arcade,  which  is  chiefly  com- 
posed of  the  quadratojugal  and  jugal. 

Below  the  post -temporal  bar  is  a  third  vacuity,  the 
post-temporal  fossa  (fig.  52,  D,  23),  bounded  above  by 
the  post-temporal  bar  and  below  by  the  exoccipital  and 
opisthotic. 

Sphenodon  and  the  Crocodilia  are  the  only  living  reptiles 
with  complete  supratemporal  and  infratemporal  arcades,  but 
they  are  both  present  in  the  extinct  Pterosauria  and  some 
Dinosauria. 

Supratemporal  fossae,  bounded  below  by  supratemporal 
arcades,  occur  in  all  reptiles  except  some  Chelonia,  the  Ophidia, 
the  Geckonidae  among  Lacertilia,  and  the  Pariasauria  and 
others  among  Theromorpha;  they  are  specially  large  in  No- 
thosaurus  among  the  Sauropterygia,  Dicynodon  among  the 
Theromorpha,  and  many  Crocodilia  and  Pterosauria.  In  some 
Dinosaurs,  such  as  Ceratosaurus,  they  are  very  small,  while 
the  infratemporal  fossae  are  correspondingly  large. 

In  Elginia1  (Theromorpha)  and  some  Chelonia,  such  as 
Chelone,  there  are  no  fossae  on  the  surface  of  the  skull, 
a  complete  false  roof  being  developed ;  in  other  Chelonia, 
such  as  Trionyx,  the  true  cranium  is  freely  visible,  the  only 
part  of  the  false  roof  developed  being  the  infratemporal 
arcade. 

In  many  reptiles  large  pre-orbital  vacuities  occur  ;  they 

1  E.  T.  Newton,  Phil.  Trans,  vol.  CLXXXIV,  B,  p.  431  (1893). 


284  THE  VERTEBRATE  SKELETON. 

are  specially  large  in  the  Pterosauria  and  in  some  of  the 
Crocodilia  and  Dinosauria  (fig.  35,  3).  In  some  Pterosauria 
they  are  confluent  with  the  orbits. 

The  premaxillae  are  usually  separate,  but  sometimes,  as  in 
some  Ophidia  (fig.  51,  1),  Chelonia,  Lacertilia  (Agamidae), 
and  Dinosaurs  (Ceratopsia)  they  are  united.  In  the  Dinosaur 
Hadrosaurus  they  are  exceedingly  large  and  spatulate.  In 
the  Rhynchocephalian  Hyperodapedon  they  are  drawn  out  into 
a  strongly  curved  beak. 

As  regards  the  mandible,  sometimes,  as  in  most  Rhyncho- 
cephalia,  Ophidia  and  Pythonomorpha,  the  rami  have  only  a 
ligamental  union ;  sometimes,  as  in  Crocodilia,  the  Rhyncho- 
sauridae  and  the  majority  of  Lacertilia,  they  are  suturally 
united.  In  Chelonia  (fig.  28,  B,  12),  and  apparently  in  Ptero- 
sauria, the  two  dentaries  are  completely  fused  together.  The 
sutures  between  the  various  bones  of  the  lower  jaw  usually 
persist,  but  in  Ophidia  those  between  the  angular,  supra - 
angular,  articular  and  coronoid  are  obliterated.  There  are 
sometimes  large  vacuities  in  the  mandible,  as  in  Theromorpha, 
Crocodilia,  and  some  Dinosauria.  In  Iguanodon,  Polyonax, 
Hypsilophodon  and  Hadrosaurus  among  Dinosaurs  the  man- 
dible has  a  predentary  or  mento-meckelian  bone  which,  in 
some  cases  at  any  rate,  was  probably  sheathed  in  a  horny 
beak. 

The  principal  part  of  the  auditory  ossicular  chain  is  formed 
by  a  rod-like  columella.  The  development  of  the  hyoid  appa- 
ratus varies,  and  it  often  happens  that  the  first  branchial  arch 
is  better  developed  than  is  the  hyoid  arch.  In  the  Crocodilia 
and  Chelonia  there  is  a  large  basilingual  plate  or  body  of  the 
hyoid  (fig.  53,  1)  ;  but  while  in  the  Crocodilia  the  first  branchial 
forms  the  only  well-developed  arch,  in  the  Chelonia  the  first 
and  second  branchial s  are  both  strongly  developed,  and  the 
hyoid  is  often  fairly  large. 


THE    SKELETON    IN    REPTILES.      THE    RIBS. 


285 


THE  RIBS. 

Ribs  are  always  present,  and  may  be  attached  to  any  of  the 
precaudal  vertebrae.  In  most  reptiles  the  posterior  cervical 
vertebrae  bear  ribs,  while  the  atlas  and  axis  are  ribless ;  in 
Crocodiles  and  Geckos,  however,  ribs  are  borne  even  by  the 
atlas  and  axis.  On  the  other  hand,  in  the  Chelonia  none  of 


FIG.  53.  HYOIDS  OF  AN  ALLIGATOR  (Caiman  latirostris)  (TO  THE  LEFT) 
AND  OF  A  GREEN  TURTLE  (Chelone  midas)  (TO  THE  RIGHT)  x  f. 
(Brit.  Mus.) 

The  cartilaginous  portions  are  dotted. 

1.  basilingual  plate  or  body  of        3.     first  branchial  arch  (anterior 

the  hyoid.  cornu). 

2.  hyoid  arch.  4.     second  branchial   arch    (pos- 

terior cornu.) 

the  cervical  vertebrae  bear  obvious  ribs.  In  the  following 
groups  the  thoracic  ribs  have  both  capitula  and  tubercula 
— Theromorpha,  Ichthyosauria,  Crocodilia,  Dinosauria,  Ptero- 
sauria.  In  the  other  groups  each  rib  articulates  by  a  single 


286          THE  VERTEBRATE  SKELETON. 

head,  and  the  position  of  the  facet  is  subject  to  a  consider- 
able amount  of  variation,  thus  in  the  Squamata  it  lies  on  the 
centrum,  and  in  the  Sauropterygia  on  the  neural  arch,  while 
in  the  Chelonia  the  rib  articulates  with  the  contiguous  parts 
of  two  centra  instead  of  directly  with  one. 

In  most  reptiles  a  greater  or  smaller  number  of  ribs  are 
united  ventrally  with  a  sternum  ;  but  in  snakes  a  continuous 
series  of  similar  ribs,  all  articulating  freely  with  the  vertebral 
column,  extends  from  the  third  cervical  vertebra  to  the  end  of 
the  trunk.  The  number  of  ribs  connected  with  the  sternum 
varies  from  three  or  four  in  Lizards  to  eight  or  nine  in  Croco- 
diles. Those  which  reach  the  sternum  are  nearly  always 
divided  into  vertebral,  sternal,  and  intermediate  portions,  and 
as  a  rule  only  the  vertebral  portion  is  completely  ossified.  In 
Crocodiles  a  number  of  sternal  ribs  are  connected  with  a 
cartilaginous  arch,  which  is  attached  to  the  hind  end  of  the 
sternum,  and  represents  the  xiphisternum.  The  sacral  ribs 
connecting  the  vertebral  column  with  the  ilia  are  very 
distinct  in  Crocodiles;  in  these  animals  and  Sphenodon  the 
vertebral  ribs  have  backwardly-projecting  uncinate  processes 
as  in  birds. 

In  the  curious  arboreal  lizard,  Draco  volans,  the  posterior 
ribs  are  long  and  straight,  and  support  a  parachute-like  expan- 
sion of  the  integument  used  in  its  long  flight-like  leaps.  In 
Chelonia  the  ribs  are  generally  combined  with  the  carapace. 

In  Ichthyosauria,  Sauropterygia,  Crocodilia  and  Sphenodon, 
abdominal  splint  ribs  occur  ;  and  probably  all  except  the  first 
of  the  paired  ossifications  forming  the  plastron  of  Chelonia  are 
of  similar  character.  Abdominal  ribs  have  quite  a  different 
origin  from  true  ribs,  for  while  true  ribs  are  cartilage  bones, 
abdominal  ribs  have  no  cartilaginous  precursors,  but  are 
simply  the  ossified  tendons  of  the  rectus  abdominalis  muscle. 


THE    SKELETON    IN    REPTILES.      THE   STERNUM. 
THE  STERNUM. 


287 


A  sternum  occurs  in  the  following  groups  of  reptiles : 
Rhynchocephalia,  nearly  all  Lacertilia,  Pythonomorpha,  Croco- 
dilia,  and  Pterosauria,  and  is  generally  more  or  less  rhomboidal 
or  shield-shaped.  In  Pterosauria  it  is  keeled  and  bears  some 
resemblance  to  that  of  birds.  It  may  have  been  replaced  by 
membrane  bone. 

The  sternum   is   absent   in    Sauropterygia,   Ichthyosauria, 


FIG.  54.     VENTRAL  VIEW  OF  THE  SHOULDER-GIRDLE  or  STERNUM  OF  A 
LIZARD  (Loemanctus    longipes]  x  2.     (After  PARKER.) 


1.  interclavicle. 

2.  clavicle. 

3.  scapula. 

4.  coracoid. 

5.  precoracoidal  process. 


6.  glenoid  cavity. 

7.  sternum. 

8.  xiphisternum. 

9.  sternal  rib. 


288          THE  VERTEBRATE  SKELETON. 

Chelonia,  Ophidia,  and  most  of  the  snake-like  Amphisbaenidae 
among  Lacertilia  ;  while  it  is  not  well  known  in  Theromorpha 
and  Dinosauria.  In  the  Sauropod  Brontosaurus,  however,  two 
rounded  bones  occur  near  the  base  of  the  coracoids,  and  these 
probably  represent  ossified  patches  in  a  sternum,  which  was 
mainly  cartilaginous ;  similar  structures  occur  in  Iguanodon. 

The  sternum  frequently  remains  wholly  cartilaginous, 
especially  in  Lacertilia ;  sometimes  it  becomes  calcified,  but 
true  ossification  does  not  as  a  rule  take  place. 

APPENDICULAR   SKELETON. 

THE  PECTORAL  GIRDLE. 

The  pectoral  girdle  is  well  developed  in  all  groups  of 
reptiles  except  the  Ophidia,  occurring  even  in  the  limbless 
Amphisbaenidae.  It  is  very  solid  in  the  Theromorpha.  As  a 
rule  all  three  cartilage  bones,  scapula,  coracoid,  and  precoracoid 
are  represented,  and  frequently  also  the  membrane  bones, — 
clavicles,  and  interclavicle. 

The  coracoids  are  generally  flat  expanded  bones,  which 
sometimes,  as  in  Sauropterygia  and  Ichthyosauria,  meet  in  a 
ventral  symphysis  ;  sometimes,  as  in  Lacertilia,  are  united  with 
the  sides  of  the  sternum.  In  Chelonia  neither  the  coracoids 
nor  precoracoids  meet  one  another,  but  their  free  ends  are 
connected  by  nbro-cartilaginous  bands.  In  Lacertilia  the 
coracoids  are  pierced  by  fenestrae. 

The  precoracoid  is  generally  represented,  but  the  Thero- 
morpha are  the  only  reptiles  in  which  it  is  separately  ossified; 
it  forms  a  well-marked  process  on  the  coracoid  in  Lacertilia 
(fig.  54,  5).  It  is  absent  in  Ichthyosauria,  and  Dinosauria, 
and  probably  in  Sauropterygia.  In  some  Lacertilia  and 
Chelonia  the  sternal  ends  of  the  coracoids  are  unossified  and 
form  epicoracoids ;  in  some  Chelonia  there  are  also  epipre- 
coracoids  ;  but  neither  these  nor  the  epicoracoids  overlap  their 
fellows  of  the  opposite  side  as  they  do  in  arciferous  Anura 
(see  p.  185).  In  some  Lacertilia  with  degenerate  limbs  the 


THE   SKELETON   IN   REPTILES.      THE   LIMBS.  289 

pectoral  girdle  is  also  much  reduced,  in  Ophisaurus  apus  the 
ventral  borders  of  the  coracoids  are  widely  separated. 

A  scapula  is  always  present,  and  is  generally  expanded 
distally,  but  in  the  Chelonia  the  distal  end  is  cylindrical.  In 
the  Theromorpha  it  has  an  acromial  process  with  which  the 
precoracoid  articulates,  and  it  is  very  large  in  Dinosauria. 
In  the  Chelonia  the  scapula  and  precoracoid  are  ossified 
continuously.  Among  the  Pterosauria,  Pteranodon  has  an 
unique  pectoral  girdle;  the  scapula  and  coracoid  are  ankylosed 
and  the  scapula  articulates  with  the  neural  spines  of  several 
ankylosed  vertebrae. 

Clavicles  occur  in  some  Theromorpha  such  as  Pariasaurus, 
and  also  in  the  Ichthyosauria,  Sauropterygia,  Rhynchocephalia, 
and  most  Lacertilia.  They  are  absent  in  the  Pterosauria,  the 
Chamaeleons  among  Lacertilia,  the  Ophidia  and  the  Crocodilia. 
They  are  wanting  too  in  the  Chelonia,  unless  the  first  pair  of 
ossifications  in  the  plastron  are  to  be  regarded  as  clavicles.  In 
the  Sauropterygia  bones  regarded  as  the  clavicles  and  inter- 
clavicle  are  generally  well  developed.  The  unpaired  ossification 
in  the  plastron  of  Chelonia  is  an  interclavicle,  and  a  repre- 
sentative of  the  same  bone  occurs  arising  from  the  sternum  in 
Pterosauria.  A  well  developed  T-shaped  interclavicle  is  found 
in  Ichthyosauria,  Rhynchocephalia,  Lacertilia,  and  some  Thero- 
morpha, such  as  Pariasaurus. 

THE  LIMBS. 

In  most  reptiles  there  are  two  pairs  of  pentedactylate 
limbs  provided  with  claws,  but  in  nearly  all  Ophidia  and 
some  Lacertilia  (Amphisbaena,  Lialis,  Anguis)  the  limbs  have 
entirely  disappeared.  In  a  few  Ophidia  such  as  Python  traces 
of  the  posterior  limbs  occur,  and  in  Chirotes  among  the  Amphis- 
baenidae  there  are  minute  anterior  limbs.  The  Lacertilians, 
Chalcides  (Seps)  and  Ophisaurus  (Bipes,  Pseudopus)  have  very 
small  posterior  limbs. 

R.  19 


290          THE  VERTEBRATE  SKELETON. 

The  limbs  are  as  a  rule  adapted  for  walking,  but  in  Ichthyo- 
sauria, Sauropterygia,  Pythonomorpha  and  some  Chelonia,  they 
have  the  form  of  swimming  paddles,  the  relative  size  of  the  manus 
and  pes  being  increased,  while  that  of  the  proximal  and  middle 
portions  of  the  limbs  is  reduced.  This  reduction  is  carried  to  its 
furthest  extent  in  the  Ichthyosauria  in  which  radius  and  ulna, 
tibia  and  fibula,  have  the  form  of  short  polygonal  bones  similar 
to  those  constituting  the  manus  and  pes.  In  the  Pythono- 
morpha the  reduction  of  the  limb  bones  is  not  quite  so  marked, 
in  the  Sauropterygia  it  is  less,  and  still  less  in  the  Chelonia. 
In  the  earlier  Ichthyosauria  too,  the  limb  bones  are  not  so 
short  as  they  are  in  the  later  forms.  The  Ichthyosaurian  limb 
is  also  remarkable,  firstly  for  the  fact  that  both  humerus  and 
femur  are  terminated  by  concave  articulating  surfaces  instead 
of  by  convex  condyles,  and  secondly  for  the  great  multiplication 
of  the  phalangeal  bones,  each  digit  being  sometimes  composed  of 
a  series  of  over  twenty.  Sometimes  too  the  number  of  series  is 
increased,  either  by  the  bifurcation  of  some  of  the  digits  or  by 
the  development  of  marginal  bones.  In  the  Sauropterygia  the 
phalanges  are  likewise  increased  above  the  normal  but  not  so 
much  as  in  Ichthyosauria.  The  humerus  and  femur  of  Sauro- 
pterygia are  noticeable  for  the  enormous  size  of  the  terminal 
epiphyses  which  form  in  each  case  by  far  the  greater  part  of 
the  bone. 

THE  ANTERIOR  LIMB. 

The  anterior  limb  is  usually  approximately  equal  in 
length  to  the  posterior,  but  in  many  Dinosauria  it  is  consider- 
ably the  shorter  of  the  two.  The  humerus  is  generally  with- 
out distinct  condyles,  but  they  are  well  developed  in  the  Thero- 
morpha,  the  Lacertilia  and  Sphenodon. 

In  the  Therornorpha,  some  Rhynchocephalia,  and  some 
Sauropterygia,  such  as  Mesosaurus,  the  humerus  has  an  ent-epi- 
condylar  foramen  ;  in  Lacertilia,  Chelonia  and  some  Dinosauria 
there  is  an  ect-epicondylar  foramen  or  groove ;  Sphenodon 


THE   SKELETON    IN    REPTILES.      PELVIC   GIRDLE.       291 

possesses  both  ent-  and  ect-epicondylar  foramina.  The  radius 
and  ulna  are  always  separate.  In  some  Chelonia,  such  as 
Chelydra,  the  carpus  has  a  very  simple  arrangement,  namely, 
a  proximal  row  of  three  bones,  the  radiale,  intermedium  and 
ulnare,  and  a  distal  row  of  five  carpalia,  with  one  bone,  the 
centrale,  between  the  two  rows.  Many  reptiles  have  a  carpus 
only  slightly  different  from  this.  Thus  the  carpus  in  Spheno- 
don  differs  mainly  in  having  two  centralia,  that  of  most  Lacer- 
tilia,  in  having  the  centrale  and  intermedium  fused. 

Crocodiles  have  a  much  reduced  carpus  with  the  radiale 
and  ulnare  considerably  elongated.  The  manus  in  Chamaeleons 
is  curiously  modified,  having  the  first  three  digits  arranged  in 
one  group  and  turned  inwards,  and  the  fourth  and  fifth  in 
another  group  turned  outwards ;  carpalia  3  and  4  are  united. 

In  the  Pterosauria  the  anterior  limbs  form  wings,  the 
phalanges  of  the  fifth  digit  being  very  greatly  elongated  to 
support  the  wing  membrane.  The  first  digit  is  vestigial  and 
the  second,  third,  and  fourth  are  clawed. 

THE  PELVIC  GIRDLE. 

The  pelvic  girdle  is  well  developed  in  all  reptiles  which 
have  posterior  limbs,  but  is  absent  or  quite  vestigial  in  Ophidia 
and  those  Lacertilia  which  have  no  posterior  limbs.  The  ilium 
and  ischium  agree  in  their  general  characters  throughout  all 
the  various  groups  of  reptiles,  but  that  is  not  the  case  with 
the  pubis. 

In  many  reptiles  such  as  Chelonia,  Ichthyosauria  and 
Lacertilia  the  ilia  are  small,  more  or  less  cylindrical  bones 
either  directed  backwards,  or  vertically  placed  as  in  the 
Chamaeleons.  In  the  Crocodilia  they  are  larger  and  more  ex- 
panded, while  in  Dinosauria  and  Pterosauria  they  are  greatly 
elongated  both  in  front  of,  and  behind,  the  acetabulum.  The 
ischia  are  generally  strongly  developed  somewhat  square  bones 
meeting  in  a  ventral  symphysis.  In  Dinosauria  the  ischium 
(fig.  35,  9)  is  a  much  elongated  and  backwardly-directed  bone, 

19—2 


292          THE  VERTEBRATE  SKELETON. 

bearing  a  forwardly  projecting  obturator  process.  In  Ptero- 
sauria  the  ischium  is  fused  with  the  ilium,  and  in  both  ptero- 
saurs and  crocodiles  the  ilium  and  ischium  are  the  only  bones 
taking  part  in  the  formation  of  the  acetabulum.  In  most 
Lacertilia  there  is  an  unpaired  structure,,  the  hypo-iachium  or 
os  cloacae  projecting  back  from  the  symphysis  ischii,  which  is 
usually  separated  from  the  symphysis  pubis  by  a  large  space, 
the  foramen  cordiforme.  In  some  Lacertilia  and  Chelonia 
there  is  a  cartilaginous  bar  dividing  the  foramen  cordiforme 
into  two  obturator  foramina ;  in  many  Chelonia  this  bar  is 
ossified.  Among  Ophidia,  Python,  Tortrix,  Typhlops  and  their 
allies  have  a  structure  representing  a  vestigial  ischio-pubis  : 
but  in  most  Ophidia  there  is  no  trace  of  the  pelvis.  In  some 
Theromorpha  all  the  bones  of  the  pelvis  are  completely  fused, 
forming  an  os  innominatum  as  in  mammals ;  the  pubes  and 
ischia  are  so  completely  fused  that  sometimes  as  in  Paria- 
saurus  even  the  obturator  foramina  are  closed. 

Concerning  the  reptilian  pubis  there  are  considerable  diffi- 
culties. Sometimes  there  is  only  a  single  pubic  structure 
present,  sometimes  there  are  two.  The  reptilian  pubis  is  best 
understood  by  comparing  the  arrangements  met  with  in  the 
various  other  groups  with  that  in  the  Orthopod  Dinosaurs 
such  as  Iguanodon.  In  Iguanodon  the  pubis  consists  of  two 
portions,  viz.  of  a  moderately  broad  pre-pubis  directed  down- 
wards and  forwards,  and  of  a  narrow  greatly  elongated  post- 
pubis  directed  backwards  parallel  to  the  ischium.  The  pubis 
is  united  to  both  ilium  and  ischium,  the  acetabulum  has  a 
large  unossified  space,  and  neither  pre-pubes  nor  post-pubes 
meet  in  ventral  symphyses.  The  arrangement  bears  a  great 
resemblance  to  that  of  Ratite  birds.  In  Lacertilia,  Chelonia, 
Rhynchocephalia  and  Ichthyosauria  together  with  Theropod 
and  Sauropod  Dinosaurs  the  pubis  corresponds  to  the  pre-pubis 
of  Iguanodon  and  is  a  more  or  less  cylindrical  bone  expanded 
at  both  ends,  meeting  its  fellow  in  a  ventral  symphysis.  In 
Chelonia  and  Lacertilia  the  pubis  bears  a  lateral  process  which 


THE    SKELETON   IN    REPTILES.    POSTERIOR   LIMB.      293 

is  homologous  with  the  post-pubis  of  Iguanodon.  In  Lacer- 
tilia  and  sometimes  in  Chelonia  there  is  a  cartilaginous  epipubis 
attached  to  the  anterior  border  of  the  pubic  symphysis  ;  this  is 
well  developed  in  the  Chamaeleons  and  Geckos.  In  Crocodilia 
there  is,  forming  the  anterior  and  ventral  portion  of  the 
acetabulum,  a  patch  of  cartilage  (fig.  49,  3)  which  is  probably 
the  true  pubis  homologous  with  that  of  lizards  and  with  the 
pre-pubis  of  Iguanodon.  The  large  bone  generally  called  the 
pubis  in  Crocodiles  is  probably  an  epipubis. 

THE  POSTERIOR  LIMB. 

The  posterior  limb  is  entirely  absent  in  some  Lacertilia  and 
in  most  Ophidia,  though  traces  occur  in  Python,  Tortrix  and 
Typldops.  In  the  Ichthyosauria,  Sauropterygia  and  Pythono- 
morpha  the  posterior  limbs  form  swimming  paddles  and  have 
been  already  referred  to. 

The  arrangement  of  the  proximal  and  middle  segments  of 
the  limb  is  fairly  constant  in  all  reptiles  with  limbs  adapted 
for  walking,  and  the  tibia  and  fibula  are  always  separate. 
The  pes  is  however  subject  to  a  considerable  amount  of  varia- 
tion, especially  as  regards  the  tarsus.  In  some  Chelonia  the 
tarsus  like  the  carpus  has  an  extremely  simple  arrangement, 
consisting  of  a  proximal  row  of  three  bones,  the  tibiale,  inter- 
medium and  fibulare,  a  ceiitrale,  and  a  distal  row  of  five  tar- 
salia.  In  most  living  reptiles,  however,  the  tibiale  and  inter- 
medium are  as  in  mammals  united,  forming  the  astragalus. 
In  Crocodiles  (fig.  48,  B,  15)  the  centrale  is  also  united  with 
the  tibiale  while  the  distal  tarsalia  are  very  slightly  developed. 
The  calcaneum  in  Crocodiles  is  drawn  out  into  a  long  process 
forming  a  heel  in  a  manner  almost  unique  among  Sauropsida. 
In  Sphenodon  and  Lacertilia  the  tibia  and  fibula  articulate 
with  a  single  large  bone  representing  the  whole  proximal  row 
of  tarsalia. 

The  pes  is  generally  pentedactylate,  but  in  some  Crocodiles 
the  fifth  digit  is  vestigial  (fig.  48,  B),  and  in  some  Dinosauria 


294  THE  VERTEBRATE  SKELETON. 

(fig.  35)  there  are  only  three  digits.  The  North  American  Dino- 
saurs present  a  continuous  series  ranging  from  a  pentedactylate 
plantigrade  form  like  Morosaurus,  to  such  a  form  as  Hallopus 
with  a  highly  digitigrade  and  specialised  pes  reduced  to  three 
functional  digits,  and  a  vestigial  fifth  metatarsal.  The  second, 
third  and  fourth  metatarsals  in  this  form  are  nearly  two- 
thirds  as  long  as  the  femur,  and  the  calcaneum  is  drawn  out 
into  a  heel  much  as  it  is  in  most  mammals. 

In  Lacertilia,  Orthopoda  and  many  Chelonia,  the  ankle 
joint  comes  to  lie  between  the  proximal  and  distal  row  of 
tarsals  as  in  birds. 


CHAPTER    XVII. 

CLASS.     AVES1. 

BIRDS  form  a  large  and  extremely  homogeneous  class  of  the 
vertebrata,  and  are  readily  distinguished  from  all  other  animals 
by  the  possession  of  an  epidermal  exoskeleton  having  the  form 
of  feathers.  Feathers  differ  from  hairs  in  the  fact  that  they 
grow  from  papillae  formed  of  both  the  horny  and  the  Mal- 
pighiaii  layer  of  the  epidermis,  which  papillae  at  first  project 
from  the  surface,  and  only  subsequently  become  imbedded  in 
pits  of  the  dermis.  A  dermal  exoskeleton  does  not  occur  in 
birds. 

The  endoskeleton  is  characterised  by  its  lightness,  the 
large  bones  being  generally  hollow ;  but  the  pneumaticity 
does  not  vary  in  proportion  to  the  power  of  flight.  The 
cervical  part  of  the  vertebral  column  is  very  long  and  flexible, 
while  the  postcervical  portion  is  generally  very  rigid,  owing 
to  the  fusion  of  many  of  the  vertebrae,  especially  in  the 
lumbar  and  sacral  regions.  The  vertebrae  are  generally  with- 
out epiphyses  to  their  centra.  The  cervical  vertebrae  in  living 
forms  have  saddle-shaped  articulating  surfaces,  and  many  of 
them  bear  ribs.  The  thoracic  ribs  in  almost  all  birds  have 
large  unciriate  processes.  The  sternum  is  very  large,  and  the 
ribs  are  always  attached  to  its  sides,  not  as  in  many  reptiles 

1  M.  Fiirbringer,  Untersuchungen  zur  Morphologic  und  Systematik  der 
Vogel,  I.  and  II.  Amsterdam,  1888.  Cf.  H.  Gadow,  Nature,  xxxix. 
1888,  pp.  150  and  177. 

T.  H.  Huxley,  "On  the  classification  of  birds."  P.  Z.  S.,  London, 
1867. 

E.  Seleuka  and  H.  Gadow,  Vogel  in  Bronn's  Classen  und  Ordnungen 
des  Thier-reichs  1869—1890. 


296          THE  VERTEBRATE  SKELETON. 

to  any  backwardly-projecting  process  or  processes.  The  sternum 
ossifies  from  two  or  more  centres. 

The  skull  is  extremely  light,  and  its  component  bones  show 
a  great  tendency  to  fuse  together  completely.  The  facial  part 
of  the  skull  is  prolonged  into  a  beak,  chiefly  formed  of  the  pre- 
maxillae;  this  beak  is  in  all  modern  birds  devoid  of  teeth, 
and  is  coated  externally  with  a  horny  epidermal  sheath.  The 
quadrate  is  large  and  freely  movable.  The  supratemporal 
arcade1  is  imperfect,  while  the  infratemporal  arcade1  is  com- 
plete. There  are  no  postorbital  or  postfrontal  bones.  Neither 
parotic  processes  nor  an  interparietal  foramen  occur.  There 
are  commonly  large  pre-orbital  vacuities.  The  palatines 
and  pterygoids  never  form  a  secondary  bony  palate  as  in 
Crocodiles.  Part  of  the  floor  of  the  skull  is  formed  by  a 
wide  basitemporal  (paired  in  the  embryo)  which  is  continued 
in  front  as  a  long  slender  rostrum ;  these  structures  have  re- 
placed the  parasphenoid  of  Ichthyopsids.  Cartilage  or  bone  is 
always  developed  in  the  sclerotic.  The  first  branchial  arch  is 
well  developed,  the  hyoid  arch  but  slightly.  The  coracoids 
are  large,  and  the  clavicles  are  nearly  always  united  forming 
ihefurc^da.  There  is  no  separate  interclavicle  and  hardly  any 
trace  of  a  precoracoid. 

The  anterior  limbs  form  wings,  and  the  manus  is  in  the 
adult  always  much  modified,  never  having  more  than  three 
digits.  The  three  bones  of  the  pelvis  are,  except  in  Archaeor- 
nithes,  always  ankylosed  together  in  the  adult,  and  the  ilium 
is  greatly  prolonged  in  front  of  the  acetabulum,  which  is 
perforated.  The  ilia  are  not  connected  with  the  sacrum  by 
ossified  sacral  ribs.  The  pubes  arid  ischia  are  directed  back- 
wards parallel  to  one  another,  and  except  in  a  very  few  forms 
never  meet  their  fellows  in  ventral  symphyses.  The  fibula 
is  generally  much  reduced.  The  proximal  tarsal  bones  are 
always  ankylosed  to  the  tibia,  and  the  distal  tarsals  to  the 
metatarsals,  so  that  the  ankle  joint  is  intertarsal.  The  first 
1  See  p.  283. 


AVES.      ARCHAEORNITHES.  297 

metatarsal  is  nearly  always  free.     The  pes  never  has  more  than 
four  digits  in  the  adult. 

The  class  Aves  is  most  conveniently  divided  into  two  sub- 
classes :  1.  Archaeornithes.  2.  Neornithes. 

Subclass  I.     ARCHAEORNITHES. 

The  only  form  referred  to  this  subclass  of  extinct  birds  is 
Archaeopteryx\  the  earliest  known  bird.  In  this  animal  the 
skeleton  does  not  seem  to  be  pneumatic.  The  cervical  and 
trunk  vertebrae  are  generally  thought  to  be  flat,  certainly 
their  articulating  surfaces  are  not  saddle-shaped.  There  is  no 
long  compound  sacrum  as  in  modern  birds.  The  tail  is  longer 
than  the  whole  body,  the  caudal  vertebrae  are  twenty  in 
number,  they  gradually  taper  as  traced  away  from  the  trunk, 
and  each  bears  a  pair  of  feathers.  The  posterior  caudal 
vertebrae  are  not  united  together  to  form  a  pygostyle.  The 
upper  jaw  bears  thirteen  pairs  of  conical  teeth,  planted  in 
distinct  sockets  in  the  maxillae  and  preinaxillae,  but  the 
mandible  has  only  three  pairs.  The  presence  of  these  teeth 
forms  the  most  essential  difference  between  the  skull  of 
Archaeopteryx  arid  that  of  modern  birds,  and  the  fact  that 
they  occur  on  the  premaxillae  renders  it  improbable  that 
a  horny  beak  was  present.  There  is  a  ring  of  ossifications 
in  the  sclerotic.  The  ribs  do  not  show  uncinate  processes, 
and  articulate  with  the  vertebrae  by  single  heads  not  divided 
into  capitula  and  tubercula.  Abdominal  ribs  appear  to  have 
been  present.  The  furcula  is  large,  and  the  scapula  has  a  well 
developed  acromion.  The  sternum  is  unknown.  The  radius 
and  ulna  are  approximately  equal  in  size.  In  the  manus  the 
first,  second  and  third  digits2  are  present,  each  terminated  by 

1  E.   Owen,   Phil.  Trans.,  vol.    CLIII.,  p.  33;  1863.      T.   H.   Huxley, 
P.  R.  S.,  vol.  xvi.,  p.  243;  1868.     C.  Vogt,  Rev.  Scient.,  ser.  2,  torn.  9, 
p.  241;  1879.     C.  H.  Hurst,  Nat.  Sci.,  vol.  in.,  p.  275;  1893;  vol.  vi., 
pp.  112,  180,  244;  1895.     W.  P.  Pycraft,  Nat.  Sci.,  vol.  v.,  pp.  350  and 
437;  1894;  and  vol.  vm.,  p.  261;  1896. 

2  According  to  Hurst  the  fourth  and  fifth  digits  are  also  present. 


298          THE  VERTEBRATE  SKELETON. 

a  claw.  The  second  digit  is  considerably  the  longest,  while 
the  third  includes  four  phalanges.  The  three  bones  of  the 
pelvis  probably  remained  distinct  throughout  life.  The  tarsals 
are  ankylosed  respectively  to  the  tibia  and  metatarsals  as  in 
other  birds.  The  metatarsals  are  ankylosed  together,  and  the 
pes  has  four  digits. 

Subclass  II.     NEORNITHES. 

To  this  subclass  may  be  referred  all  known  birds  except 
Archaeopteryx.  They  all  agree  in  having  a  short  tail  whose 
component  vertebrae  are  commonly  ankylosed  together  form- 
ing a  pygostyle.  The  three  metacarpals  do  not  all  remain 
distinct.  The  bones  of  the  pelvis  are  ankylosed  together, 
and  to  a  large  though  variable  number  of  vertebrae.  There 
are  three  orders,  the  Ratitae,  Odontolcae,  and  Carinatae. 

Order  1.     RATITAE. 

The  Ratitae  differ  from  Archaeopteryx  and  the  great 
majority  of  Carinatae  in  being  flightless.  The  bones  are 
generally  not  pneumatic,  containing  marrow  instead  of  air, 
in  the  Ostrich  however  they  are  very  pneumatic.  The  tail 
is  short  and  the  posterior  caudal  vertebrae  are  generally 
ankylosed  together  forming  a  pygostyle.  The  pectoral  girdle 
has  comparatively  a  much  smaller  size  than  in  Carinatae, 
clavicles  are  small  or  absent,  and  the  scapula  and  coracoid 
lie  nearly  in  the  same  straight  line.  The  ilium  and  ischium 
do  not  as  in  Carinatae  unite  posteriorly,  and  enclose  a 
foramen  except  in  very  old  Rheas  and  Emeus.  The  quadrate 
articulates  with  the  cranium  by  a  single  head.  The  vomers 
unite  and  form  a  broad  plate,  separating  the  palatines,  ptery- 
goids  and  basisphenoidal  rostrum. 

The  anterior  limbs  are  greatly  reduced  in  size  or  even 
absent,  while  the  posterior  limbs  are  greatly  developed  and 
adapted  for  running.  The  tibia  and  fibula  are  quite  distinct. 


AVES.      RATITAE.  299 

Many  ornithologists  agree  that  the  various  forms  grouped 
together  as  Ratitae  are  not  all  very  closely  allied  to  one  another, 
that  they  resemble  one  another  mainly  in  having  lost  the  power 
of  flight,  and  do  not  form  a  natural  group. 

The  Ratitae  include  the  following  groups  : — 

JBpyomithes1,  huge  extinct  birds  from  Madagascar. 

Apteryges,  including  the  Apteryx  of  New  Zealand. 

Dinornithes2,  the  Moas,  huge  extinct  birds  from  New 
Zealand,  and  some  of  the  neighbouring  islands. 

Megistanes,  including  the  Cassowaries  (Casuarius)  of  Aus- 
tralia, New  Guinea,  and  some  of  the  neighbouring  islands ; 
and  the  Emeus  (Dromaeus)  of  Australia. 

Rheornithes,  including  the  Rheas  of  S.  America. 

Struthiornithes,  including  the  Ostriches (Struthio)  now  living 
in  Africa,  and  found  fossil  in  N.  India  and  Samos. 

Order  2.     ODONTOLCAE. 

This  order  includes  only  an  extinct  N.  American  bird 
ffesperornis3.  The  jaws  are  provided  with  a  series  of  sharp 
teeth  placed  in  continuous  grooves,  but  the  premaxillae  are 
toothless,  and  were  probably  sheathed  in  a  horny  beak.  The 
rami  of  the  mandible  are  not  ankylosed  together  in  front. 
The  skeleton  is  not  pneumatic.  The  cervical  vertebrae  have 
saddle-shaped  articulating  surfaces  as  in  ordinary  birds,  and 
the  thoracic  vertebrae  are  not  ankylosed  together.  The  tail 
is  comparatively  long,  and  formed  of  twelve  vertebrae  with 
only  slight  indications  of  a  pygostyle.  The  ribs  have  uncinate 
processes.  The  anterior  limb  is  quite  vestigial,  being  reduced 
to  a  slender  humerus.  The  posterior  limb  is  very  powerful 
and  adapted  for  swimming. 

1  See  C.  W.  Andrews,  P.  Z.  S.,  1894,  p.  108. 

2  See  T.  J.  Parker,  2V.  Zool.  Soc.  London,  vol.  xiti.,  pt.  2,  1895,  and 
F.  W.  Button,  several  papers  in  Tr.  N.  Zealand  Inst.,  1893  and  1895. 

3  See  0.  C.  Marsh.    Odontornithes.   A  monograph  of  the  extinct  toothed 
birds  of  N.  America.     Newhaven,  1880. 


300  THE    VERTEBRATE    SKELETON. 

Order  3.     CARINATAE. 

This  order  includes  the  vast  majority  of  living  birds. 
The  cervical  vertebrae  have  saddle-shaped  articulating  surfaces 
(except  in  the  Ichthyornithiformes).  The  posterior  caudal 
vertebrae  are  ankylosed  forming  a  pygostyle.  The  quadrate 
articulates  with  the  cranium  by  a  double  head.  In  all  except 
the  Tinamidae  the  vomers  are  narrow  behind  and  not  inter- 
posed between  the  palatines,  pterygoids  and  basisphenoidal 
rostrum.  The  sternum  has  a  median  keel,  and  the  anterior 
limbs  are  in  the  great  majority  of  cases  adapted  for  flight. 
Clavicles  are  well  developed,  and  the  scapula  and  coracoid  are 
nearly  at  right  angles  to  one  another.  The  various  groups 
into  which  the  Carinatae  are  divisible  are  shown  in  the  table 
on  pp.  40 — 42.  Their  special  characters  will  not  be  dealt  with. 

FIG.  55.  Gallus  barikiva  var.  domesticus.  THE  LEFT  HALF  OF  THE  SKELETON. 
The  skull,  vertebral  column,  and  sternum  are  bisected  in  the  median 
plane.  (After  Marshall  and  Hurst.) 

A,  acetabulum.  B,  cerebral  fossa.  CB,  cerebellar  fossa.  CL,  clavicle.  CO,  coracoid. 
CR,  cervical  rib.  C  l  =  one,  first  cervical  vertebra.  FE,  femur.  HC,  ventral  end  of  clavicle. 
HU,  humerus.  HY,hyoid.  IF,  ilio-sciatic  foramen.  IL,  ilium.  IS,  ischium.  L,  lachrymal. 
MC  3,  postaxial  metacarpal.  MN,  mandible.  MS,  xiphoid  processes.  MT,  tarso-metatarsus. 
MT  1,  first  metatarsal.  N,  nasal.  OP,  optic  foramen.  P,  premaxilla.  PB,  pubis.  PL, 
palatine.  PY,  pygostyle.  R,  radius.  RC,  radial  carpal.  S,  keel  of  sternum.  SC,  scapula. 
T,  tibio-tarsus.  TH  4,  fourth  thoracic  vertebra.  U,  ulna.  UC,  ulnar  carpal.  UP,  uncinate 
process.  Z,  infra-orbital  bar.  1,  2,  3,  4,  first,  second,  third  and  fourth  digits  of  pes.  3,  pre- 
axial,  4,  middle,  and  5,  postaxial  digit  of  manus. 


AVES.      CARINATAE. 


301 


CHAPTER   XVIII. 

THE   SKELETON    OF    THE    WILD    DUCK   (Anas 
boschas). 

I.     EXOSKELETOK 

The  exoskeleton  of  the  Duck  and  indeed  of  all  birds  is 
entirely  epidermal  in  origin.  Its  most  important  part  consists 
of  feathers,  but  it  includes  also  the  following  horny  struc- 
tures : — 

(a)  scales,  which  cover  the  toes  and  tarso-metatarsus ; 

(b)  claws,  which  are  attached  to  the  distal  phalanges  of 
the  toes  and  of  the  pollex ; 

(c)  the  wide  beak,  which  sheaths  both  upper  and  lower 
jaws,  and  whose  edges  are  raised  into  lamellae,  which  act  as 
strainers. 

FEATHERS. 

A  well  developed  feather,  such  as  one  of  the  large 
quill  feathers  of  the  wing  or  tail,  consists  of  the  following 
parts :  A  main  stem,  the  scapus,  which  forms  the  axis 
running  along  the  whole  length  of  the  feather,  and  is  divided 
into  (1)  a  proximal  hollow  cylindrical  portion,  the  calamus  or 
quill,  and  (2)  a  distal  solid  portion,  the  rachis  or  shaft,  which 
is  square  in  section,  flexible  and  grooved  along  its  ventral 
surface,  and  bears  a  number  of  lateral  processes,  the  barbs. 
The  calamus  which  is  partly  imbedded  in  a  pit  in  the  dermis, 


SKELETON  OF  THE  WILD  DUCK.   THE  FEATHERS.  303 

bears  two  holes :  one,  the  inferior  umbilicus,  is  at  its 
proximal  end,  and  into  it  enters  a  vascular  outgrowth  from  the 
dermis;  the  other,  the  superior  umbilicus,  lies  on  the 
ventral  surface  at  the  junction  of  the  calamus  and  scapus. 

The  barbs  are  a  series  of  narrow  elastic  plates,  attached 
by  their  bases  to  the  rachis,  and  with  their  edges  looking 
upwards  and  downwards.  The  barbs  are  connected  together 
by  a  number  of  smaller  processes,  the  barbules,  which  inter- 
lock with  one  another  by  means  of  booklets,  and  bear  the 
same  relation  to  the  barbs  that  the  barbs  do  to  the  rachis. 
The  barbs  and  barbules,  together  with  the  rachis,  constitute 
the  vexillum  or  vane  of  the  feather.  Any  feather  having 
the  above  type  of  structure  is  called  a  penna  or  a  contour 
feather,  from  the  fact  that  it  helps  to  produce  the  contour  of 
the  body. 

VARIETIES  OF  FEATHERS. 

1.  Pennae.  There  are  two  kinds  of  pennae  or  contour 
feathers. 

(a)  The  quills.  These  form  the  large  feathers  of  the 
wing  and  tail.  They  are  divided  into  two  groups,  the 
remiges,  or  wing  quills,  and  the  rectrices,  or  tail  quills. 

The  remiges l  include  three  sets  of  feathers,  the  primaries 
or  metacarpo-digitals,  which  are  attached  to  the  bones  of 
the  manus,  the  secondaries  or  cubitals,  which  are  attached 
to  the  ulna,  and  the  humerals,  which  are  attached  to  the 
humerus. 

The  primaries  differ  from  all  the  other  quill  feathers 
in  having  the  posterior  half  of  the  vane  much  wider  than  the 
anterior  half.  They  are  ten  in  number,  and  of  these  six, 
the  metacarpal  quills  (fig.  57,  14),  are  attached  to  the  second 
and  third  metacarpals,  one,  the  ad-digital  (fig.  57,  15),  to  the 
phalanx  of  the  third  digit,  two,  the  mid-digitals  (fig.  57,  16). 
to  the  first  phalanx  of  the  second  digit,  and  two,  the  pre-digitals 

1  See  E.  S.  Wray,  P.  Z.  S.,  1887,  p.  343. 


304 


THE  VERTEBRATE  SKELETON. 


(fig.  51,  17),  to  the  second  phalanx  of  the  second  digit.  One 
of  the  pre-digitals  is  very  small,  and  is  called  the  remicle 
(fig.  57,  11). 


FIG.  56.     THE  WING  OF  A  WILD  DUCK  (Anas  bosclias). 

The  upper  figure  shows  the  dorsal  side  of  a  right  wing,  the  lower  figure 

the  ventral  side  of  a  left  wing,     x  ^.     (Brit.   Mus.) 

1.  scapulars.  6.     metacarpo-digitals      or      pri- 

2.  tectrices  marginales.  maries. 

3.  tectrices  minores.  7.     tectrices  mediae. 

4.  bastard  wing.  8.     cubitals  or  secondaries. 

5.  tectrices  majores.  9.     pennae  humerales. 

10.     pennae  axillares. 

In  addition,  a  group  of  three  quill  feathers  is  attached  to 
the  first  digit,  constituting  the  bastard  wing  or  ala  spuria 
(fig.  56,  4). 

The  secondaries  or  cubitals  (fig.  56,  8)  form  a  group  of 
seventeen  feathers,  attached  to  the  ulna  ;  they  are  shorter  than 


SKELETON  OF  THE  WILD  DUCK.   THE  FEATHERS.  305 

the  primaries,  and  do  not  have  the  posterior  half  of  the  vane 
much  wider  than  the  anterior  half. 

The  humerals  (figs.  56,  9  and  57,  12)  form  a  group  of 
eight  small  feathers,  of  varying  length,  attached  to  the  anterior 
half  of  the  humerus. 


B 


FIG.  57.     WINGS  OF  A  WILD  DUCK  WITH  THE  COVERTS  REMOVED 

(Anas  boschas).      x  -|. 

A.     Eight  wing  seen  from  the  dorsal  side.     B.     Left  wing  disarticulated 
and  seen  from  the  ventral  side.     (Brit.  Mus.) 


1.  humerus. 

2.  radius. 

3.  ulna. 

4.  radial  carpal. 

5.  ulnar  carpal. 

6.  first  phalanx  of  first  digit. 

7.  second  metacarpal. 

8.  third  metacarpal. 

9.  first  phalanx  of  second  digit. 

R. 


10.  second     phalanx    of    second 

digit. 

11.  remicle. 

12.  pennae  humerales. 

13.  cubitals  or  secondaries. 

14.  metacarpal  quills. 

15.  ad-digital. 

16.  mid-digitals. 

17.  pre-digital. 

20 


306          THE  VERTEBRATE  SKELETON. 

(b)  The  tectrices  or  coverts  are  short  feathers,  which 
cover  over  the  quills  of  the  rectrices  and  remiges,  and  clothe 
the  body  generally.  Their  barbules  are  less  developed  than  is 
the  case  with  the  quill  feathers,  so  that  the  barbs  separate 
readily  from  one  another,  especially  at  the  base  of  the  vane. 
The  nomenclature  of  the  various  patches  of  coverts  on  the 
wings  is  seen  in  fig.  56.  A  small  patch  of  backwardly-directed 
feathers  surrounding  the  external  auditory  opening  are  known 
as  the  auriculars. 

2.  The  filophimes  are  rudimentary  feathers,  consisting 
of  a  minute  stem  and  slightly  developed  vane.     They  are  left 
in  the  skin  after  the  other  feathers  have  been  removed. 

3.  The  phimulae,  or  down  feathers,  have  the  stem  very 
slightly  developed,  while  the  barbs  are  soft  and  free  from  one 
another.     They  are  distributed  all  over  the  body,   not  only 
among  the  contour  feathers,  but  also  over  the  spaces  (apteria) 
which  bear  no  contour  feathers. 

In  the  young  bird  the  rudiments  of  the  new  feathers  are 
formed  at  the  bases  of  the  embryonic  down  feathers,  and  as 
they  grow  they  push  them  out  from  the  skin.  The  embryonic 
down  feathers  however  remain  attached  to  the  apices  of  the 
new  feathers  till  these  have  reached  a  length  of  about  an 
inch;  they  are  then  shed. 

II.     ENDOSKELETON. 

As  compared  with  that  of  the  Turtle  or  Crocodile,  the 
endoskeleton  of  the  Duck  is  characterised  by  : 

1.  The  great  lightness  of  the  bones,  many  of  which  con- 
tain air  cavities. 

2.  The  tendency  to  become  ankylosed  together  shown  by 
many  of  the  bones. 

3.  The  modification  of  the  anterior  limbs  and  girdle  for 
the  purpose  of  flight. 


SKELETON  OF  THE  WILD  DUCK.     VERTEBRAL  COLUMN.    307 

1.     THE  AXIAL  SKELETON. 

This,  as  in  other  vertebrates,  is  divisible  into — 

A.  The  vertebral  column. 

B.  The  skull. 

C.  The  ribs  and  sternum. 

A.     THE  VERTEBRAL  COLUMN. 

The  vertebral  column  of  the  duck,  like  that  of  the  great 
majority  of  birds,  presents  a  number  of  well-marked  character- 
istics, contrasting  strongly  with  those  of  the  generality  of 
higher  vertebrates.  The  centra  are  always  without  epiphyses. 
The  neck  is  exceedingly  long,  about  as  long  as  all  the  rest  of 
the  vertebral  column  put  together,  and  is  remarkable  for  its 
flexibility.  The  trunk  portion  of  the  vertebral  column  on  the 
other  hand  is  characterised  by  extreme  rigidity,  and  the 
marked  tendency  shown  by  the  component  vertebrae  to  fuse 
together  into  one  almost  continuous  mass.  The  most  rigid 
part  of  the  vertebral  column  is  that  to  which  the  pelvis  is 
united,  as  no  less  than  seventeen  vertebrae  take  part  in  the 
union.  The  tail  of  the  duck,  like  that  of  all  living  birds,  is 
very  short,  arid  the  posterior  caudal  vertebrae  are  united 
togther,  forming  the  pygostyle.  The  vertebral  column  may 
be  divided  into  cervical,  thoracic,  lumbar,  sacral,  and  caudal 
regions,  but  the  boundaries  between  the  several  regions  are  ill- 
defined. 

THE  CERVICAL  VERTEBRAE. 

All  the  vertebrae  anterior  to  the  first  one  that  bears  a  rib 
meeting  the  sternum  are  regarded  as  cervical  vertebrae. 
There  are  therefore  sixteen  cervical  vertebrae,  the  last  two  of 
which  bear  well  developed  ribs.  All  are  freely  movable  on 
one  another. 

As  a  typical  cervical  vertebrae,  any  one  from  the  fifth  to 
the  ninth  may  be  taken.  The  vertebra  is  rather  elongated, 
and  is  very  lightly  and  strongly  made,  its  most  characteristic 

20—2 


308  THE  VEKTEBRATE  SKELETON. 

feature  being  the  shape  of  the  articulating  surfaces  of  the 
centra,  which  are  generally  described  as  saddle-shaped.  The 
anterior  surface  is  convex  from  above  downward,  and  concave 
from  side  to  side,  while  the  posterior  and  more  prominent 
surface  is  concave  from  above  downwards  and  convex  from 
side  to  side.  The  neural  arch  is  low,  and  is  drawn  out  into  a 
slight  blade-like  neural  spine.  Its  base  is  deeply  notched  on 
both  sides  posteriorly  for  the  exit  of  the  spinal  nerves.  Above 
these  notches  it  is  drawn  out  into  two  rather  prominent 
diverging  processes,  which  bear  the  postzygapophyses,— 
two  flattened  surfaces  which  look  downwards  and  outwards. 
The  transverse  processes  form  irregular  outgrowths  from 
the  anterior  two-thirds  of  the  sides  of  the  vertebra ;  each 
projects  for  a  short  distance  downwards  and  outwards,  and 
is  terminated  posteriorly  by  a  short  backwardly-projecting 
spine.  The  transverse  processes  are  shown  by  development 
to  ossify  from  separate  centres,  and  are  therefore  to  be 
regarded  as  cervical  ribs,  and  each  is  perforated  at  its  base  by 
a  canal  for  the  passage  of  the  vertebral  artery.  Above  the 
anterior  end  of  the  vertebrarterial  canal  are  a  pair  of 
thickened  outgrowths,  which  bear  upwardly  and  inwardly 
directed  prezygapophyses.  Each  transverse  process  is 
perforated  near  its  middle  by  a  prominent  foramen  through 
which  passes  a  vein  which  is  connected  with  the  jugular  vein. 

The  third  and  fourth  cervical  vertebrae  resemble  the  suc- 
ceeding ones  in  most  respects,  but  have  small  hypapophyses, 
and  the  neural  spines  are  less  blade-like.  The  posterior 
cervical  vertebrae  (tenth  to  sixteenth)  differ  somewhat  from 
the  middle  ones.  They  are  shorter  and  more  massive,  the 
neural  arch  is  much  shorter,  being  deeply  notched  in  the 
middle  line  in  front  and  behind.  The  transverse  processes  arise 
from  the  anterior  half  of  the  vertebra  only,  and  in  the  eleventh 
vertebra  each  is  drawn  out  below  into  a  pair  of  rather  promi- 
nent downwardly  and  inwardly  directed  processes.  In  the 
twelfth  vertebra  these  processes  have  almost  coalesced,  and 


SKELETON  OF  THE  WILD  DUCK.     VERTEBRAL  COLUMN.    309 

in  the  thirteenth  vertebra  they  have  coalesced  completely, 
forming  a  prominent  hypapophysis.  In  the  succeeding 
vertebrae  this  hypapophysis  rapidly  decreases  in  size. 

The  fifteenth  and  sixteenth  cervical  vertebrae  resemble  the 
succeeding  thoracic  vertebrae,  having  short  thick  centra  and 
prominent  squarely  truncated  neural  spines  ;  the  sides  of  the 
neural  arches  are  very  deeply  notched.  The  fifteenth  vertebra 
has  a  short  transverse  process,  perforated  by  a  wide  vertebrar- 
terial  foramen,  but  this  foramen  is  absent  in  the  sixteenth. 
The  transverse  processes  of  the  fifteenth  vertebra  bear  two 
facets  for  the  articulation  of  the  capitulum  and  tuberculum  of 
the  rib.  The  sixteenth  vertebra  has  its  tubercular  facet  on 
the  transverse  process,  but  the  capitular  facet  is  borne  on  the 
centrum. 

The  second  or  axis  vertebra  is  small,  and  has  the  centrum 
drawn  out  into  a  comparatively  very  large  hypapophysis.  The 
posterior  articulating  surface  of  the  centrum  is  saddle-shaped, 
the  anterior  nearly  flat  :  above  it  the  centrum  is  prolonged 
into  the  prominent  odontoid  process,  which  is  shown  by 
development  to  be  the  detached  centrum  of  the  atlas.  The 
neural  arch  is  deeply  notched  in  the  middle  line  in  front,  and 
at  the  sides  behind.  It  is  drawn  out  posteriorly  into  a  wide 
massive  outgrowth,  which  overhangs  the  third  vertebra  and 
bears  the  downwardly-directed  postzygapophyses.  The  pre- 
zygapophyses  are  situated  at  the  sides  of  the  anterior  end  of 
the  neural  arch,  and  look  directly  outwards.  The  transverse 
processes  are  very  slightly  developed,  and  are  pierced  by  the 
vertebrarterial  canals. 

The  atlas  vertebra  is  a  very  slight  ring-like  structure, 
thickened  ventrally  and  bearing  in  front  a  prominent  concave 
cavity  for  articulation  with  the  occipital  condyle  of  the  skull. 
Posteriorly  it  bears  a  more  or  less  flattened  surface  for  arti- 
culation with  the  centrum  of  the  axis.  It  surrounds  a  large 
cavity  partially  divided  into  a  larger  dorsal  portion,  which  is 
the  neural  canal,  and  a  smaller  ventral  portion  which  lodges 


310          THE  VERTEBRATE  SKELETON. 

the  odontoid  process.  The  sides  of  the  atlas  are  pierced  by 
the  vertebra rterial  canals,  above  which  there  are  two  slight 
backwardly-projecting  outgrowths  bearing  the  postzygapophyses 
on  their  inner  faces. 

THE  THORACIC  VERTEBRAE. 

The  thoracic  region  includes  all  the  vertebrae  bearing  free 
ribs,  except  the  first  two,  viz.  those  whose  ribs  do  not  reach 
the  sternum.  There  are  seven  thoracic  vertebrae.  The  first 
four  have  centra  with  saddle-shaped  articulating  surfaces,  but 
are  more  or  less  firmly  united  together  by  their  neural  spines  ; 
the  last  two  are  completely  ankylosed  by  their  centra  to  the 
lumbar  vertebrae. 

Each  of  the  first  five  vertebrae  has  a  prominent,  vertical, 
abruptly  terminated  neural  spine,  and  straight  transverse 
processes.  The  zygapophyses  and  articulating  surfaces  at  the 
ends  of  the  centra  are  well  developed.  The  third,  fourth,  fifth, 
and  sixth  vertebrae  have  verv  prominent  hypapophyses.  The 
articular  facets  for  the  ribs  are  well  marked,  those  for  the  tu- 
bercula  lying  at  the  free  ends  of  the  transverse  processes,  and 
those  for  the  capitula  at  the  sides  of  the  anterior  ends  of  the 
centra.  The  sixth  and  seventh  thoracic  vertebrae  are  firmly 
fused  by  their  centra  and  neural  arches  to  one  another  and 
to  the  lumbar  vertebrae  behind,  and  by  their  transverse  pro- 
cesses to  the  ilia.  The  sixth  has  its  centrum  terminated  in 
front  by  a  saddle-shaped  articulating  surface,  and  bears  a  pair 
of  prominent  prezygapophyses.  Its  transverse  processes  and 
centrum  bear  facets  for  the  tubercula  and  capitula  of  the  ribs 
respectively.  In  the  seventh  vertebra  the  tubercular  facet  is 
wanting. 

THE  SACRUM. 

The  sacrum  generally  consists  of  seventeen  vertebrae 
fused  with  one  another  and  with  the  ilia.  Their  number  may 
be  reckoned  from  the  number  of  foramina  for  the  exit  of  spinal 
nerves.  The  two  most  anterior  of  these  vertebrae  bear  ribs 


SKELETON   OF   THE   WILD   DUCK.      THE   SACRUM.     311 

and  have  been  already  described  with  the  other  thoracic 
vertebrae.  Their  neural  spines  and,  those  of  the  four  succeed- 
ing vertebrae  are  fused  together,  forming  a  continuous  crest 
of  bone  completely  united  laterally  with  the  ilia.  The  trans- 
verse processes  of  all  these  six  vertebrae  are  well  developed, 

A  B 


FlG.   58.       A,   DORSAL   AND  B,    VENTRAL  VIEW    OF   THE  PELVIS  AND  SACRUM  OF 

A  DUCK  (Anas  boschas). 

1.  ilium.  4.     pectineal  process. 

2.  ischium.  5.    lumbar  vertebrae. 

3.  pubis.  6.     true  sacral  vertebrae. 

but  those  of  the  posterior  two  (fig.  58,  B,  5)  are  much  the 
stoutest.  The  next  three  vertebrae  have  broad  centra,  but 
their  transverse  processes  are  very  slightly  developed  and  have 
no  ventral  elements.  These  seven  vertebrae  belong  to  the 
lumbar  series.  The  remaining  eight  vertebrae  have  well- 
developed  transverse  processes,  which  in  the  case  of  the  first 
three  or  four  are  divisible  into  dorsal  and  ventral  elements. 
All  the  dorsal  elements  are  united  to  form  a  pair  of  flattened 
plates,  partially  separated  by  a  series  of  foramina  from  a 


312 


THE  VERTEBRATE  SKELETON. 


median  plate  formed  by  the  united  neural  arches.  Laterally 
they  are  continuous  with  the  ischia.  The  first  two  of  this 
series  of  vertebrae  are  shown  by  their  relation  to  the  nerves 
to  be  the  true  sacrals  (fig.  58,  B,  6),  the  remaining  six  belong- 
ing to  the  caudal  series. 

Behind  them  come  the  six  free  caudal  vertebrae,  succeeded 
by  a  terminal  piece,  the  pygostyle,  formed  of  a  number  of 
vertebrae  fused  together  ;  this  bears  the  rectrices  or  tail  quills. 


15 


18,. 


FIG.  59.     SKULL  OF  A  DUCK  (Anas  boschas).     x  1. 
A.     Dorsal  view  of  the  cranium.        B.     Palatal  view  of  the  mandible. 

C.     The  Hyoid. 
For  numbers  see  Fig.  60. 
B.     THE  SKULL. 

The  skull  of  the  duck,   like  that  of  birds  in  general,  is 
characterised  (1)  by  its  lightness,  (2)  by  the  contrast  between 


SKELETON   OF   THE   WILD    DUCK. 


THE   SKULL.       313 
11 


FIG.  60.     A.     Ventral  view  of  the  cranium  of  a  Duck  (Anas  boschas). 
B.     Cranium  and  mandible  seen  from  the  left  side,      x  1. 


1.  maxilla.  22. 

2.  premaxilla.  23. 

3.  anterior  nares.  24. 

4.  nasal  process   of    premaxilla 

(fig.  59).  25. 

5.  nasal. 

6.  frontal  (fig.  59).  26. 

7.  lachrymal. 

8.  postfrontal  process. 

9.  parietal  (fig.  59).  27. 

10.  jugal. 

11.  quadratojugal. 

12.  quadrate. 

13.  condyle  of  mandible. 

14.  posterior  articular  process. 

15.  dentary  at  symphysis.  \  28. 

16.  basi-hyal.  I  (fig.          29. 

17.  uro-hyal.  59).       30. 

18.  basibranchial.  31. 

19.  vomer.  I. 

20.  palatine.  mina. 

21.  pterygoid. 


anterior  palatine  foramen. 

basitemporal. 

foramen  leading  into  tympanic 
cavity. 

bristle  inserted  into  posterior 
opening  of  carotid  canal. 

bristle  inserted  into  posterior 
opening  of  Eustachian 
canal. 

bristle  emerging  through  an- 
terior opening  of  carotid 
canal.  Close  by  is  seen  the 
bristle  emerging  through 
the  anterior  opening,  of  the 
Eustachian  canal. 

fenestral  recess. 

maxillo-palatine. 

lambdoidal  crest. 

rostrum. 

II.  IV.  V.  IX.  X.  nerve  fora- 


314          THE  VERTEBRATE  SKELETON. 

the  bones  of  the  cranium  proper  and  those  forming  the  '-rest 
of  the  skull,  for  the  bones  forming  the  cranium  proper  are 
closely  fused  together,  the  sutures  between  them  being  nearly 
all  completely  obliterated  in  the  adult,  while  the  bones  form- 
ing the  face  are  loosely  connected  with  the  cranium  proper ; 

(3)  by  the  prolongation  of  the  face  into  a  long  toothless  beak ; 

(4)  by  the  size  of  the  orbits,  and  their  position  entirely  in 
front  of  the  cranium,  so  that   they  are   separated  from   one 
another  only  by  a  thin  interorbital  septum. 

For  purposes  of  description  the  skull  may  be  divided  into 

(1)  The  cranial  portion. 

(2)  The  facial  portion. 

(3)  The  mandible. 

(4)  The  hyoid. 

(1)     THE  CRANIAL  PORTION. 

This  is  a  rounded  box  expanded  dorsally  and  posteriorly, 
but  tapering  antero-ventrally.  In  the  young  skull  the  divi- 
sional lines  between  the  several  bones  can  be  easily  seen, 
but  in  the  adult  they  are  quite  obliterated. 

(a)  The  dorsal  surface  is  rounded,  expanded  in  front  and 
behind,  but  encroached  upon  in  the  middle  by  the  cavities  of  the 
orbits.    There  is  a  prominent  divisional  line  in  front,  separating 
it  from  the  facial  part  of  the  skull.      It  is  formed  mainly  by 
the  frontal  (fig.  59,  A,  6)  and  parietal  bones,  but  the  frontals 
diverge  a  little  anteriorly  and  enclose  between  them  the  ends 
of  the  nasal  processes  (fig.  59,  A,  4)  of  the  premaxillae.     Just 
in  front  of  the  orbit   the   outer  margins  of  the  frontals  are 
either  notched  or  pierced  by  a  pair  of  foramina. 

(b)  At  the  posterior  end  of  the  cranium  the  most  promi- 
nent feature  is  the  large,  almost  circular  foramen  magnum, 
through  which  the  spinal  cord  and  brain  communicate ;  this  in 
young  birds  is  seen  to  be  bounded  by  four  distinct  bones,  dor- 
sally by  the  supra-occipital,  ventrally  by  the  basi-occipital, 
and  laterally  by  the  exoccipitals. 


SKELETON  OF  THE  WILD  DUCK.   THE  SKULL.   315 

The  basi-occipital  forms  the  main  part  of  a  prominent 
convex  knob,  the  occipital  condyle,  with  which  the  atlas 
articulates.  The  occipital  condyle  is  slightly  notched  above, 
and  the  ventral  surface  of  the  cranium  is  deeply  pitted  just 
in  front  of  it ;  the  exoccipitals  also  contribute  slightly  to  its 
formation.  Slightly  in  front  of  and  ventral  to  the  foramen 
magnum  is  a  small  foramen  through  which  the  hypoglossal 
nerve  leaves  the  cranial  cavity. 

The  supra-occipital  is  separated  from  the  parietal  by  a 
suture  line  along  which  run  a  pair  of  prominent  ridges,  the 
lambdoidal  crests  (fig.  60,  B,  30).  There  are  often  a  pair  of 
prominent  vacuities  in  the  supra-occipital  dorsal  to  the  foramen 
magnum.  The  epi-otics  and  opisthotics  become  completely 
fused  with  the  bones  of  the  occipital  segment  at  a  very  early 
stage. 

(c)  The  ventral  surface  of  the  cranium  is  wide  behind, 
where  it  is  formed  by  a  broad '  transverse  membrane  bone,  the 
basitemporal  (fig.  60,  A,  23),  the  sides  of  which  are  fused  with 
the  auditory  capsules.  Slightly  in  front  of  and  an  eighth  of 
an  inch  external  to  the  hypoglossal  foramen  the  cranial  wall  is 
pierced  by  a  pair  of  foramina  through  which  the  tenth  or 
pneumogastric  nerves  leave  (fig.  60,  A,  X).  At  the  sides 
of  the  basitemporal  are  a  pair  of  depressions,  the  tympanic 
recesses,  in  each  of  which  are  three  holes.  Straight  lines 
joining  these  holes  would  form  an  isosceles  triangle  with  its 
apex  directed  forwards.  Of  the  two  holes  at  the  base  of  the 
triangle,  the  one  nearer  the  middle  line  and  leading  into  the 
cranial  cavity,  is  for  the  exit  of  the  ninth  or  glossopharyngeal 
nerve  (fig.  60,  A,  IX),  it  lies  just  in  front  of  the  pneumogastric 
foramen.  The  more  external  leads  into  the  tympanic  cavity, 
while  the  more  anterior  at  the  apex  of  the  triangle  is  the 
posterior  opening  of  the  carotid  canal  (fig.  60,  A,  25), 
which  traverses  the  base  of  the  cranium,  and  during  life 
lodges  the  carotid  artery. 

The  anterior  end  of  the  basitemporal  is  pierced  near  the 


316          THE  VERTEBRATE  SKELETON. 

middle  line  by  a  pair  of  holes,  the  anterior  openings  of  the 
Eustachian  canals  \  while  just  in  front  of  these  and  a  little 
further  removed  from  the  middle  line  are  the  anterior  openings 
of  the  carotid  canals.  Bristles  passed  in  through  the  posterior 
openings  of  the  carotid  canals  will  emerge  here  (fig.  60,  A,  27). 
In  front  of  the  basitemporal  the  base  of  the  cranium  is  formed 
by  the  rostrum  (fig.  60,  A,  31),  or  thickened  basal  portion  of 
the  iiiterorbital  septum  ;  this  bears  two  prominent  surfaces 
with  which  the  pterygoids  articulate.  In  some  kinds  of 
duck  these  surfaces  are  borne  by  well-marked  basi-pterygoid 
processes. 

(d)  The  side  of  the  cranium.  At  the  base  of  the  posterior 
end  is  seen  the  deep  tympanic  cavity.  The  dorsal  part  of 
this  is  divided  by  a  vertical  partition  into  two  halves  ;  of  these 
the  more  anterior  is  the  larger,  and  forms  a  deep  funnel- 
shaped  cavity,  the  posterior  opening  of  the  Eustachian 
canal  (fig.  60,  B,  26).  A  bristle  passed  into  this  opening- 
emerges  through  the  anterior  opening  of  the  Eustachian  canal. 
The  more  posterior  of  the  two  is  the  fenestral  recess  (fig.  60, 
B,  28),  and  is  in  its  turn  divided  by  a  slender  horizontal  bar 
into  a  dorsal  hole,  the  fenestra  ovalis,  and  a  ventral  hole, 
the  fenestra  rotunda.  During  life  the  fenestra  ovalis  lodges 
the  proximal  end  of  the  columellar  chain.  Lying  at  the 
outer  side  and  slightly  dorsal  to  the  tympanic  cavity  is  a  deep 
depression,  the  lateral  tympanic  recess,  and  immediately 
in  front  of  this  is  the  articular  surface  for  the  quadrate. 
The  tympanic  cavity  is  bounded  below  by  the  basitemporal, 
posteriorly  by  the  exoccipital,  and  above  by  the  squamosal,  a 
membrane  bone,  which  roofs  over  a  good  deal  of  the  side  of 
the  cranium,  and  bears  ventrally  a  prominent  surface  with 
which  the  quadrate  articulates.  Just  in  front  of  this  is  a 
large  round  hole,  the  trigeminal  foramen  (fig.  60,  B,  Y), 
behind  which  the  squamosal  is  drawn  out  into  a  short  process. 

In  front  of  the  squamosal  there  is  a  prominent  forwardly- 
projecting  postfrontal  process  (fig.  60,  8),  which  ossifies 


SKELETON  OF  THE  WILD  DUCK.   THE  SKULL.   317 

from  a  different  centre  from  that  forming  the  squamosal,  but 
in  the  adult  is  completely  fused  with  it. 

The  orbit  forms  a  large  more  or  less  hemispherical  cavity 
which  lodges  the  eyeball.  It  is  separated  from  its  fellow  of 
the  opposite  side  by  an  imperfect  partition,  the  interorbital 
septum.  In  the  young  skull  it  is  seen  to  be  bounded  above  by 
the  frontal,  with  which  the  lachrymal  (fig.  60,  7)  is  fused 
anteriorly,  forming  a  large  backwardly-projecting  process  \ 
while  behind  it  is  bounded  by  the  alisphenoid.  The  inter- 
orbital  septum  is  formed  by  the  ossification  and  coalescence  of 
the  mesethmoid  in  front,  with  the  orbitosphenoid  behind, 
and  the  rostrum  below.  The  boundary  of  the  orbit  below 
is  very  imperfect,  the  zygomatic  arch  being  incomplete. 

The  interorbital  septum  is  pierced  by  the  very  prominent 
optic  foramen  (fig.  60,  B,  2),  just  behind  which  are  the  two 
much  smaller  foramina  for  the  exit  of  the  oculomotor  and 
pathetic  (fig.  60,  B,  IV)  nerves,  the  more  anterior  being  that 
for  the  oculomotor. 

Above  and  slightly  in  front  of  the  optic  foramen  is  a 
median  opening,  the  olfactory  foramen.  This  leads  into 
the  cranial  cavity  behind,  and  in  front  is  continued  forwards 
as  a  groove  between  the  interorbital  septum  and  the  frontal. 


(2)     THE  FACIAL  PART  OF  THE  SKULL. 

This  includes  the  olfactory  capsule  and  associated  bones, 
and  the  upper  jaw. 

The  bones  associated  with  the  olfactory  capsules  are  the 
nasals  and  vomer.  The  nasals  (figs.  59  and  60,  5)  lie  on  the 
dorsal  surface  immediately  in  front  of  the  cranium,  and  are 
separated  from  one  another  by  the  nasal  processes  of  the  pre- 
maxillse.  Each  is  completely  fused  in  the  adult  with  the 
corresponding  maxilla  and  premaxilla,  the  three  bones  together 
forming  the  boundary  of  the  anterior  nares.  The  vomer  (fig. 
60,  19)  is  unpaired  and  forms  a  small  median  vertical  plate 


318  THE   A7ERTEBRATE    SKELETON. 

lying  ventral  to  the  anterior  continuation  of  the  interorbital 
septum. 

The  bones  of  the  upper  jaw  consist  on  each  side  of  two 
slender  arcades  which  in  front  converge  and  are  attached  to 
the  large  beak,  while  behind  they  diverge  but  are  united  by 
the  quadrate. 

The  inner  arcade  is  formed  by  the  pterygoid  and  palatine. 
The  pterygoid  (fig.  60,  21)  is  a  short  flattened  bone,  which 
articulates  behind  with  the  quadrate,  and  on  its  inner  side 
with  a  large  flattened  surface  borne  by  the  rostrum,  in  front 
it  meets  the  palatine,  or  sometimes  ends  freely  with  a  long 
antero-dorsally  directed  point. 

The  palatine  (fig.  60,  20)  is  a  slender  irregular  bone  flat- 
tened dorso-ventrally  at  its  anterior  end  where  it  articulates 
with  the  beak,  and  laterally  behind.  It  gives  off  at  its 
posterior  end  a  process,  which  is  sometimes  united  with  the 
vomer,  sometimes  projects  forwards,  and  meets  its  fellow 
dorsal  to  the  vomer.  In  the  large  space  between  it  and  the 
vomer  is  the  opening  of  the  posterior  nares. 

The  premaxillae  (figs.  59  and  60,  2)  are  very  large,  and 
form  nearly  a  third  of  the  big  shovel-shaped  beak.  They  con- 
stitute the  inner,  and  part  of  the  front  boundary  of  the  an- 
terior nares,  and  send  back  a  pair  of  nasal  processes  which 
partially  separate  the  nasals  from  one  another. 

The  outer  arcade  forms  the  slender  suborbital  bar, 
and  consists  mainly  of  two  rod-like  bones,  which  in  the  adult 
are  completely  fused  together.  The  posterior  of  these  is  the 
quadratojugal  (figs.  59  and  60,  11)  which  articulates  with  tlie 
quadrate,  the  anterior  is  the  small  and  slender  jugal  or  malar 
(figs.  59  and  60,  10).  The  extreme  anterior  part  of  the  bar  is 
formed  by  the  maxilla.  The  main  part  of  the  maxilla  how- 
ever lies  anterior  to  the  suborbital  bar,  and  extends  forwards 
along  the  side  of  the  premaxilla  forming  all  the  lateral  part  of 
the  beak  (figs.  59  and  60,  1);  it  also  sends  inwards  a  plate, 
the  maxillo-palatine  (fig.  60,  A,  29),  which  completely  fuses 


SKELETON  OF  THE  WILD  DUCK.   THE  SKULL.   319 

with  its  fellow  in  the  middle  line,  and  forms  the  posterior 
boundary  of  the  anterior  palatine  foramen.  The  term 
desmognathous  describes  the  condition  of  the  skull  in 
which  the  maxillo-palatines  fuse  with  one  another  in  the 
middle  line  in  this  way. 

The  quadrate  (fig.  60,  12),  which  unites  the  two  arcades 
behind,  is  a  stout  irregular  four-cornered  bone  forming  the 
suspensorium.  It  articulates  by  its  dorso-posterior  corner 
with  the  squamosal,  and  by  its  antero-internal  corner  with  the 
pterygoid.  The  middle  of  its  ventral  surface  forms  a  hemi- 
spherical knob  with  which  the  mandible  articulates,  while  its 
dorso-anterior  border  is  drawn  out  into  a  long  point  which 
extends  towards  the  interorbital  septum. 

(3)     THE  MANDIBLE. 

The  mandible  or  lower  jaw  consists  of  two  rami  which 
are  flattened  and  fused  together  in  the  middle  line  in  front, 
while  behind  they  diverge  from  one  another  and  articulate 
with  the  quadrates. 

Each  ramus  is  composed  of  five  bones  fused  together,  one 
being  a  cartilage  bone,  and  the  other  four  membrane  bones. 
The  articular  is  the  only  cartilage  bone  of  the  mandible, 
it  bears  the  double  condyle  (figs.  59  and  60,  13)  or  concave 
articular  surface  for  the  quadrate,  and  is  drawn  out  behind 
into  a  large  hooked  posterior  articular  process.  The  ar- 
ticular is  also  drawn  out  into  a  prominent  process  on  each 
side  of  the  articular  surface  for  the  quadrate,  and  is  marked 
by  a  deep  pit  opening  posteriorly.  The  articular  is  continuous 
in  front  with  Meckel's  cartilage  which  forms  the  original 
cartilaginous  bar  of  the  lower  jaw,  and  is  ensheathed  by  the 
membrane  bones.  Of  these  the  supra-angular  forms  the  upper 
part  of  the  mandible  in  front  of  the  articular,  its  dorsal  sur- 
face is  drawn  out  into  a  small  coronoid  process,  its  outer 
surface  also  bearing  a  prominent  process.  The  angular  is 


320  THE  VERTEBRATE  SKELETON. 

a  small  bone  which  underlies  the  articular  and  supra-angular 
on  the  inner  side  of  the  jaw.  The  dentary  (fig.  59,  15)  forms 
the  anterior  half  of  each  ramus,  and  is  the  largest  bone  of  the 
mandible  ;  it  is  fused  with  its  fellow  at  the  symphysis  in  front, 
and  extends  back  below  the  supra-angular.  The  splenial  is  a 
small  bone  lying  along  the  middle  half  of  the  inner  side  of 
each  ramus  of  the  mandible. 

(4)     THE  HYOID. 

With  the  hyoid  apparatus  is  included  the  eolumella. 
This  forms  a  minute  rod  of  bone,  one  end  of  which  is  ex- 
panded and  fits  into  the  fenestra  ovalis,  while  the  other  end,, 
terminated  by  a  triradiate  piece  of  cartilage,  is  attached 
to  the  tympanic  membrane.  The  structure  is  as  a  whole 
homologous  with  the  auditory  ossicles  of  mammals  and  the 
hyomandibular  of  fish. 

The  hyoid  consists  of  a  median  unpaired  portion,  formed 
of  two  pieces  of  bone,  the  basi-hyal  (fig.  59,  C,  16)  in  front, 
and  the  uro-hyal  (fig.  59,  C,  17)  behind,  the  two  being  placed 
end  to  end  and  terminated  anteriorly  by  an  unpaired  carti- 
laginous plate,  the  os  entoglossum.  At  the  posterior  end 
there  come  off"  a  pair  of  long  posterior  cornua,  each  of 
which  consists  of  two  pieces,  a  longer  basibranchial  (fig.  59, 
C,  18),  and  a  shorter  ceratobranchial.  For  the  homology  of 
these  parts  see  p.  336. 

THE  RIBS  AND  STERNUM. 

The  last  two  cervical  vertebrae  bear  long  movable  ribs 
which  articulate  by  distinct  capitular  and  tubercular  processes, 
but  do  not  meet  the  sternum.  The  thoracic  ribs  are  eight  in 
number,  and  each  is  divisible  into  a  vertebral  and  a  sternal 
portion.  The  first  five  thoracic  ribs  are  flattened  curved  bars 
of  bone,  which  articulate  by  a  prominent  capitulum  with 
the  centrum  of  the  corresponding  vertebra,  and  by  a  tuber- 
eulum  with  the  transverse  process.  Projecting  backwards 
from  each  is  a  large  hooked  uncinate  process.  The  last  three 


SKELETON   OF   THE    WILD    DUCK.      THE    STERNUM.      321 

ribs  which  are  without  uncinate  processes,  become  progressively 
more  slender,  and  in  the  eighth  the  tubercular  processes  are  lost. 
The  sternal  portions  of  the  ribs  are  imperfectly  ossified 
pieces,  short  and  comparatively  thick  in  the  case  of  the  anterior 
ribs,  longer  and  more  slender  in  the  case  of  the  posterior  ribs. 

THE    STERNUM1. 

The  sternum  or  breast  bone  is  exceedingly  large  in  the 
Duck,  as  in  all  birds,  and  projects  back  far  beyond  the  thorax  over 
much  of  the  anterior  part  of  the  abdomen.  It  is  an  irregularly 
oblong  plate  of  bone,  abruptly  truncated  behind,  somewhat 
concave  dorsally,  and  drawn  out  ventrally  into  a  prominent  keel, 
the  carina,  which  projects  for  some  distance  forwards  beyond 
the  body  of  the  sternum,  and  tapers  off  gradually  behind. 
The  point  where  the  carina  joins  the  body  of  the  sternum  is  at 
the  anterior  end  drawn  out  into  a  small  process,  the  rostrum2. 
Just  dorso-lateral  to  this  are  a  pair  of  deep  grooves,  the 
coracoid  grooves,  with  which  the  coracoids  articulate. 

The  sides  of  the  sternum  are  drawn  out  in  front  into  a 
pair  of  short  blunt  costal  processes ;  and  just  behind  these 
are  a  series  of  seven  surfaces  with  which  the  ends  of  the 
sternal  ribs  articulate.  Immediately  behind  these  surfaces 
the  sides  are  produced  into  a  pair  of  long  backwardly-pro- 
jecting  xiphoid  processes  which  nearly  meet  processes  from 
the  posterior  end  of  the  sternum. 

2.     THE  APPENDICULAR  SKELETON. 

This  consists  of  the  skeleton  of  the  anterior  and  posterior 
limbs  and  of  their  respective  girdles. 

A.     THE  PECTORAL  GIRDLE  \ 

The  pectoral  girdle  in  almost  all  birds  is  strongly  constructed 
and  firmly  united  to  the  sternum.  It  consists  of  three  bones, 
a  dorsal  element,  the  scapula,  a  posterior  ventral  element,  the 
coracoid,  and  an  anterior  ventral  element,  the  clavicle. 

1  Cp.  fig.  63. 

2  Often  called  the  manubrium,  but  not  homologous  with  the  manu- 
brium  of  the  mammalian  sternum. 

R.  21 


322          THE  VERTEBRATE  SKELETON. 

The  scapula  forms  a  long  curved  flattened  bone  expanded 
at  its  anterior  end,  where  it  meets  the  coracoid,  and  lying 
across  the  ribs  at  its  tapering  posterior  end.  It  helps  to  form 
the  imperfect  glenoid  cavity,  with  which  the  humerus  arti- 
culates. The  coracoid,  a  shorter  but  stouter  bone  than  the 
scapula,  has  its  upper  end  or  head  thickened  and  bears  on  its 
posterior  border  an  irregular  surface,  with  part  of  which  the 
scapula  articulates,  while  the  rest  forms  part  of  the  glenoid 
cavity.  The  inner  border  of  the  coracoid  adjoining  the  arti- 
cular facet  for  the  scapula  is  produced  into  a  strong  process 
which  helps  to  complete  the  foramen  triosseum,  a  space 
lying  between  the  adjoining  ends  of  the  scapula  and  coracoid, 
through  which  the  tendon  of  the  second  pectoral  muscle  passes. 
The  lower  part  of  the  coracoid,  which  is  much  flattened  and 
expanded,  and  abruptly  truncated  posteriorly,  articulates 
with  the  coracoid  groove  of  the  sternum.  The  clavicle  is  a 
thickened  curved  membrane  bone,  which  is  fused  with  its 
fellow  in  the  middle  line  below,  the  two  forming  the  furcula 
or  merrythought.  Its  dorsal  end  is  drawn  out  into  a  process 
which  articulates  with  the  coracoid. 

THE  ANTERIOR  LIMB  OR  WING. 

This  consists  of  three  parts,  a  proximal  part,  the  upper  arm 
or  brachium,  a  middle  part,  the  fore- arm  or  antibrachmm, 
and  a  distal  part,  the  maims.  When  extended  for  flight  the 
parts  lie  almost  in  the  same  straight  line,  but  when  at  rest  they 
are  folded  on  one  another  in  the  form  of  a  Z,  the  brachium  and 
manus  pointing  backwards,  and  the  anti brachium  forwards. 
When  extended  for  flight  the  surfaces  and  borders  of  the  wing- 
correspond  in  position  with  those  of  the  primitive  vertebrate 
limb1,  the  pre-axial  border  being  directed  forwards  and  the  post- 
axial  backwards,  while  the  dorsal  and  ventral  surfaces  look 
respectively  upwards  and  downwards.  But  when  the  wing  is 
at  rest,  the  humerus  as  it  extends  backwards  becomes  slightly 
rotated,  so  that  its  dorsal  surface  looks  more  inwards  than 
1  See  p.  28. 


SKELETON  OF  THE  WILD  DUCK.   THE  WING.   323 

upwards,  while  the  dorsal  surface  of  the  antibrachium  looks 
partially  outwards  and  upwards,  and  that  of  the  manus  mainly 
outwards. 

The  brachium  or  upper  arm  contains  only  a  single  bone, 
the  humerus  (fig.  57,  1).  This  is  a  large  nearly  straight  bone 
expanded  at  both  ends.  The  proximal  end  is  specially  ex- 
panded, forming  two  tuberosities,  and  a  large  convex  head 
articulating  with  the  glenoid  cavity.  The  pre-axial  tube- 
rosity  is  the  smaller  of  the  two,  but  is  continued  by  a 
prominent  deltoid  ridge,  which  extends  for  a  very  short 
distance  down  the  shaft.  The  postaxial  tuberosity  is  the 
larger,  and  below  it  there  is  a  very  deep  pit,  the  pneumatic 
foramen,  which  leads  into  an  air  cavity  in  the  shaft  of  the 
bone.  The  shaft  is  long  and  straight,  and  at  the  distal  end 
of  the  bone  is  the  trochlea  with  two  convex  surfaces,  one 
pre-axial  with  which  the  radius  articulates,  the  other  post- 
axial  for  the  ulna. 

The  fore-arm  or  antibrachium  consists  of  two  bones, 
the  radius  and  ulna.  These  are  of  nearly  equal  length,  and 
are  separated  from  one  another  by  a  considerable  space  except 
at  their  terminations. 

The  radius  (fig.  57,  2),  the  pre-axial  and  smaller  bone,  is 
straight  and  fairly  stout ;  its  proximal  end  articulates  with 
the  humerus  by  a  slightly  cupped  surface,  while  its  distal  end, 
which  articulates  with  the  carpus,  is  convex  and  somewhat 
expanded. 

The  ulna  (fig.  57,  3)  is  longer,  stouter,  and  slightly  curved. 
Its  proximal  end  is  expanded,  forming  two  surfaces  which 
articulate  with  the  trochlea  of  the  humerus ;  behind  them  it 
is  drawn  out  into  a  short  blunt  olecranon  process.  Its 
distal  end  is  less  expanded,  and  articulates  with  the  carpus 
and  also  with  the  radius. 

The  Manus.  This  includes  the  carpus  or  wrist,  and  the 
hand. 

The  Carpus.  While  in  the  embryo  the  carpus  consists 

21—2 


324          THE  VERTEBRATE  SKELETON. 

of  five  distinct  elements  arranged  in  a  proximal  row  of  two 
and  a  distal  row  of  three,  in  the  adult  only  the  proximal 
bones  can  be  clearly  distinguished,  the  distal  ones  having 
become  completely  ankylosed  with  the  metacarpals  to  form 
the  carpometacarpus. 

The  two  distinct  carpal  bones  are  the  radial  carpal  and 
the  ulnar  carpal.  The  radial  carpal  (fig.  57,  4)  is  a  small 
somewhat  cubical  bone,  wedged  in  between  the  manus  and 
the  radius  and  ulna.  The  ulnar  carpal  (fig.  57,  5)  is  a 
somewhat  larger,  more  irregular  bone,  lying  adjacent  to  the 
end  of  the  ulna.  It  is  deeply  notched  to  receive  the  carpo- 
metacarpus. 

The  hand.  In  the  adult  bird  the  hand  is  in  a  much 
modified  condition ;  only  the  first  three  digits  are  represented, 
and  the  metacarpals  are  all  fused  with  one  another  and  with 
the  distal  carpalia  to  form  the  carpo-metacarpus. 

The  most  prominent  part  of  the  carpo-metacarpus  is  formed 
by  the  second  metacarpal  (fig.  57,  7),  a  stout,  straight  bone 
expanded  at  both  ends.  The  third  metacarpal  (fig.  57,  8) 
is  a  more  slender  curved  bone  fused  at  both  ends  with  the 
second  metacarpal.  The  first  metacarpal  forms  simply  a 
small  projection  on  the  radial  side  of  the  proximal  end  of  the 
second  metacarpal. 

The  phalanges.  The  first  digit  or  pollex  includes  two 
phalanges,  the  distal  one  being  very  small  and  bearing  a  claw. 

The  second  digit  includes  three  phalanges,  the  proximal 
one  being  somewhat  flattened.  The  third  digit  has  a  single 
small  phalanx. 

THE  PELVIC  GIRDLE. 

The  bones  constituting  the  pelvic  girdle  are  not  only  as  in 
other  higher  vertebrates  ankylosed  together  forming  the  in- 
nominate bones,  but  are  also  ankylosed  with  a  series  of  some 
seventeen  sacral  and  pseudosacral  vertebrae.  The  acetabulum 
(fig.  61,  5)  with  which  the  head  of  the  femur  articulates  is 
incompletely  ossified. 


SKELETON    OF   THE    WILD   DUCK.      PELVIC   GIRDLE.      325 


The  ilium  (figs.  58  and  61,  1)  is  the  largest  bone  of  the 
pelvis.  It  forms  a  long  flattened  plate  extending  for  a  con- 
siderable distance  both  in  front  of  and  behind  the  acetabulum, 
and  is  fused  along  its  whole  length  with  the  transverse  pro- 
cesses and  neural  spines  of  the  sacral  and  pseudosacral  verte- 
brae. It  forms  more  than  half  the  acetabulum,  above  and 


FIG.  61.     LATERAL   VIEW  OF   THE  PELVIS  AND  SACRUM  OF  A  DUCK  (Anas 


boschas)  x 


1.  ilium. 

2.  ischium. 

3.  pubis. 

4.  pectineal  process. 


5.  acetabulum. 

6.  ilio-sciatic  foramen. 

7.  fused  vertebrae. 

8.  antitrochanter. 


behind  which  it  is  produced  to  form  a  process,  the  antitro- 
chanter (fig  61,  8),  with  which  the  great  trochanter  of  the 
femur  articulates. 

The  ischium  (figs.  58  and  61,  2)  is  a  flattened  bone  which 
forms  about  one-third  of  the  acetabulum,  and  lies  ventral  to  the 
posterior  part  of  the  ilium.  Its  anterior  portion  is  separated 
from  the  ilium  by  the  large  oval  ilio-sciatic  foramen  (fig. 
61,  6),  while  behind  this  the  two  bones  are  completely  fused. 

The  pubis  (figs.  58  and  61,  3)  is  a  very  long  slender  bar 
of  bone  which  forms  only  a  very  small  part  of  the  acetabulum 
and  runs  back  parallel  to  the  ventral  surface  of  the  ischium 
with  which  it  is  loosely  connected  at  its  posterior  end.  For 
the  greater  part  of  their  length  the  two  bones  are  separated  by 


326  THE   VERTEBRATE    SKELETON. 

the  long  narrow  obturator  foramen.  Behind  the  ischium 
the  pubis  is  produced  into  a  long  curved  downwardly-project- 
ing process,  and  in  front  of  the  acetabulum  it  bears  a  short 
blunt  pectineal  or  pre-pubic  process  (fig.  61,  4)  probably 
homologous  with  the  pre-pubis  of  Orthopod  Dinosaurs.  The 
remainder  of  the  pubis  is  homologous  with  the  post-pubis  of 
Orthopod  Dinosaurs. 

THE  POSTERIOR  LIMB. 

The  leg  of  the  bird  is  somewhat  differently  constructed  from 
that  of  other  vertebrates  owing  to  the  fact  that  there  is  no 
free  tarsus,  the  proximal  tarsals  having  fused  with  the  tibia, 
and  the  distal  with  the  metatarsals. 

The  thigh  consists  of  a  single  bone,  the  femur.  The  femur 
is  a  comparatively  short  bone  with  a  straight  shaft  and  ex- 
panded ends.  The  proximal  end  bears  on  its  inner  side  a 
rounded  head,  which  articulates  with  the  acetabulum.  On  its 
outer  side  is  an  irregular  outgrowth,  the  great  trochanter, 
while  between  the  two  is  the  surface  which  meets  the  antitro- 
chanter  of  the  ilium.  The  posterior  end  also  is  expanded 
and  marked  by  a  wide  groove  which  lodges  the  patella.  On 
each  side  of  the  groove  is  a  strong  condylar  ridge  for  articu- 
lation with  the  tibia.  The  external  condyle  is  deeply  grooved 
behind  for  articulation  with  the  fibula. 

The  crus  or  shin  consists  of  two  separate  bones,  (1)  the 
tibio-tarsus,  formed  by  the  fusion  of  the  tibia  with  the  proxi- 
mal row  of  tarsals,  and  (2)  the  fibula. 

The  tibio-tarsus  is  a  thick  straight  bone  nearly  twice  as 
long  as  the  femur.  Both  ends  of  the  bone  are  considerably 
expanded.  The  proximal  end  bears  two  slight  depressions 
which  articulate  with  the  condyles  of  the  femur,  and  a  third 
depression  which  partly  lodges  the  patella.  The  proximal  end 
of  the  anterior  or  extensor  surface  is  drawn  out  into  a  very 
prominent  cnemial  crest  which  bends  over  towards  the  post- 
axial  side  of  the  bone ;  a  slight  ridge  is  continued  from  it  all 


SKELETON  OF  THE  WILD  DUCK.   THE  PES.    327 

the  way  down  the  shaft.  The  proximal  part  of  the  shaft  of 
the  tibio-tarsus  bears  a  roughened  ridge  with  which  the  fibula 
is  closely  connected.  The  distal  end  is  expanded  and  rotated 
outwardly  and  forms  a  prominent  pulley-like  surface  which 
articulates  with  the  tarso-metatarsus. 

The  fibula  is  reduced  to  the  proximal  portion  only,  which 
is  expanded  and  articulates  with  a  depression  behind  the 
external  condyle  of  the  femur.  The  fibula  further  extends 
about  a  third  of  the  way  down  the  shaft  of  the  tibio-tarsus. 
The  patella  or  knee-cap  is  a  sesamoid  bone  due  to  an  ossi- 
fication in  the  tendon  of  the  extensor  muscles  of  the  leg. 

The  ankle  joint  lies  between  the  proximal  and  distal 
tarsals  which  as  previously  mentioned  fuse  respectively  with 
the  tibia  and  metatarsus. 

The  Pes.  The  pes  includes  four  digits,  and  consists  of  the 
tarso-metatarsus  and  the  phalanges.  The  proximal  tarsals 
which  are  fused  with  the  tibia  also  really  belong  to  the  pes. 

The  tarso-metatarsus  is  a  strong  straight  bone  nearly  as 
long  as  the  femur,  and  is  formed  by  the  fusion  of  the  distal 
tarsals  with  the  second,  third  and  fourth  metatarsals.  The 
proximal  end  of  the  bone  is  expanded  and  bears  two  facets  for 
articulation  with  the  tibio-tarsus,  and  near  them  on  the  pos- 
terior surface  is  a  large  roughened  projection.  The  lines  of 
junction  between  the  several  metatarsals  are  marked  along 
the  shaft  by  slight  ridges.  At  the  distal  end  of  the  bone  the 
three  metatarsals  diverge  from  one  another  arid  each  bears  a 
prominent  convex  pulley-like  surface.  The  first  metatarsal 
is  reduced  to  the  distal  end,  which  tapers  to  a  point  proximally, 
and  is  attached  by  ligaments  near  the  distal  end  of  the  tarso- 
metatarsus. 

The  digits.  Four  digits  are  present,  each  consisting  of  a 
metatarsal  (already  described)  and  a  certain  number  of  pha- 
langes, the  terminal  one  being  in  each  case  clawed.  The  first 
digit  or  hallux  has  two  phalanges,  the  second  three,  the  third 
four,  and  the  fourth  five. 


CHAPTER   XIX. 

GENERAL   ACCOUNT   OF   THE   SKELETON   IN 
BIRDS. 

EXOSKELETON. 

The  epidermal  exoskeleton  of  birds  is  very  greatly  de- 
veloped, feathers  constituting  its  most  important  part. 

Three  kinds  of  feathers  are  found,  viz.  (a)  pennae  including 
quills  and  coverts,  (6)  down  feathers  or  plumulae,  and  (c)  filo- 
plumes  which  are  rudimentary  feathers.  The  structure  of 
the  different  kinds  of  feathers  is  described  on  pp.  303 — 306. 

Sometimes  a  fourth  class  of  feathers,  the  semiplumae,  is 
recognised.  They  have  the  stems  of  pennae,  and  the  downy 
barbs  and  barbules  of  plumulae. 

In  most  birds  the  pennae  are  riot  uniformly  distributed 
over  the  whole  surface  of  the  body,  but  are  confined  to  certain 
tracts,  the  pterylae ;  while  the  intervening  spaces  or  apteria 
are  either  bare  or  covered  only  with  down  feathers.  In  some 
birds,  however,  such  as  the  Ratitae  a*nd  the  Penguins,  pennae 
are  evenly  distributed  over  the  whole  body. 

In  many  birds  the  calamus  or  quill  bears  two  vexilla  or 
vanes,  the  second  of  which,  called  the  attershaft  or  hypo- 
rachis,  is  generally  much  the  smaller,  and  is  attached  to  the 
under  surface  of  the  main  vexillum.  In  the  Moas,  Emeu  and 
Cassowary  the  two  vexilla  in  the  adult  bird  are  nearly  equal 
in  size ;  though  in  the  nestling  Emeu  one  is  much  longer  than 
the  other.  The  aftershaft  is  very  small  in  most  Passeres  and 
gallinaceous  birds,  but  is  comparatively  large  in  Parrots,  Gulls, 


THE    SKELETON    IN   BIRDS.      THE    EXOSKELETON.      329 

Herons  and  most  birds  of  prey.  It  is  absent  or  extremely 
small  in  the  Ostrich,  Apteryx,  Rhea,  Pigeons,  Owls,  Anseres, 
and  others. 

The  quill  feathers  include  two  groups,  the  remiges  or 
wing  quills,  and  the  rectrices  or  tail  quills.  In  most  birds 
the  primary  remiges,  or  those  which  are  attached  to  the  bones 
of  the  manus,  are  ten  or  eleven  in  number,  and  are  set  in 
grooves  in  the  bones,  being  firmly  attached  to  them.  In  the 
Ostrich  however  the  primaries  are  little  specialised  in  character 
and  are  as  many  as  sixteen  in  number.  They  are  also  less 
definitely  attached  to  the  bones ;  as  their  ends  do  not  lie  in 
grooves  in  the  bones,  but  project  beyond  them. 

The  secondary  quills  or  those  attached  to  the  ulna  vary 
much  in  number  according  to  the  length  of  the  bone.  The 
large  dark  quills  in  the  wings  of  Cassowaries  are  the  second- 
aries. 

The  wing  of  Penguins  is  very  little  differentiated.  It 
is  covered  at  the  margin  by  overlapping  scales  which  gradually 
merge  into  scale-like  feathers  at  the  proximal  end.  The  wing 
of  the  Penguin  has  nothing  comparable  to  the  remiges  of  other 
birds. 

In  some  birds,  such  as  Herons  (Ardea),  there  occur  in 
places  plumulae  of  a  peculiar  kind,  which  grow  persistently 
and  whose  summits  break  off  into  fine  powder  as  fast  as  they 
are  formed.  These  feathers  are  known  as  powder -down 
feathers.  They  occur  also  in  some  Parrots  and  are  then 
scattered  indiscriminately  all  over  the  body. 

Other  exoskeletal  structures  besides  feathers  are  commonly 
well  developed.  Thus  the  extremities  of  the  jaws  are  sheathed 
in  horny  beaks  whose  form  varies  enormously  according  to 
the  special  mode  of  life. 

In  ducks  and  geese  the  beak  with  the  exception  of  the 
anterior  end  is  soft,  and  its  edges  are  raised  into  lamellae, 
while  in  the  Mergansers  these  lamellae  become  pointed  pro- 
cesses supported  by  bony  outgrowths.  These  lamellae  act  as 


330          THE  VERTEBRATE  SKELETON. 

strainers.      In  Parrots  and  Hawks,  on  the  other  hand,  nearly 
the  whole  of  the  beak  is  hard. 

The  toes  and  tarso-metatarsus  are  usually  featherless  and 
are  covered  either  with  granular  structures  or  with  well- 
formed  scales.  The  toes  are  nearly  always  provided  with 
claws,  and  these  vary  in  correlation  with  the  character  of  the 
beak.  Claws1  also  sometimes  occur  on  the  manus.  Thus 
Archaeopteryx  and  some  Ostriches  and  Rheas  have  claws  on 
all  three  digits.  Most  Ostriches  and  Rheas,  and  many  Anseres 
and  birds  of  prey,  have  them  on  the  first  two  digits,  while  the 
Secretary  bird  (Gypogeranus)  and  many  fowls,  ducks,  and  birds 
of  prey,  especially  kestrels,  have  a  claw  only  on  the  pollex. 
In  the  Cassowary,  Emeu,  Apteryx  and  some  Ostriches  and 
Rheas  only  the  second  digit  is  clawed. 

Claws  should  not  be  confounded  with  spurs,  which  are 
conical  horny  structures  developed  on  bony  outgrowths  of 
the  radial  side  of  the  carpus,  metacarpus,  or  metatarsus. 
They  occur  in  a  number  of  birds,  but  are  most  commonly 
developed  in  gallinaceous  birds,  by  which  they  are  used  for 
fighting.  A  single  spur  occurs  on  the  metacarpus  in  Mega- 
podius,  in  Palamedea,  in  Parra  jacana  and  in  ffoplopterus 
spinosus,  the  Spur-winged  plover.  The  Derbiaii  Screamer, 
Chauna  derbiana,  has  two  metacarpal  spurs,  borne  on  the 
first  and  second  metacarpals.  The  Spur-winged  goose,  Plec- 
tropterus  gambensis,  has  a  carpal  spur  borne  on  the  radial 
carpal.  Metatarsal  spurs  are  quite  common. 

The  male  Solitaire  (Pezophaps)  has  large  bony  excrescences 
on  the  wrist  which  may,  like  spurs,  have  been  sheathed  in 
horn  and  used  for  fighting. 

Teeth  do  not  occur  in  any  living  birds,  but  conical  teeth 
imbedded  in  separate  sockets  are  present  in  Archaeopteryx 
and  Ichthyornis,  while  in  Hesperornis  similar  teeth  occur  im- 
planted in  continuous  grooves  in  the  mandibles  and  maxillae, 
the  premaxillae  being  toothless. 

1  W.  K.  Parker,  Phil.  Trans,  vol.  179,  p.  385, 1888 ;  and  Ibis,  1888,  p.  124. 


THE  SKELETON  IN  BIRDS.   THE  ENDOSKELETON.  331 


Except  that  teeth  are  partly  dermal  in  origin,  a  dermal 
exoskeleton  is  quite  unrepresented  in  birds. 

ENDOSKELETON. 

Perhaps  the  most  striking  feature  of  the  endoskeleton  of 
birds  is  its  pneumaticity.  In  the  embryo  all  the  bones  con- 
tain marrow,  but  as  growth  proceeds  this  becomes  replaced  by 
air  to  a  variable  extent  in  different  forms.  In  all  birds  some 
part  of  the  skeleton  is  pneumatic.  Many  small  birds  and 
Apteryx  and  Penguins  among  larger  ones  have  air  only  in  the 
skull ;  in  Pigeons  air  is  present  in  all  the  bones  except  the 
caudal  vertebrae,  the  leg  bones,  and  those  of  the  antibrachium 
and  manus ;  in  Hornbills  every  bone  contains  air. 


FIG.  62.     THIRD  CERVICAL  VERTEBRA  OF  AN  OSTRICH  (Struthio  camelus). 
x  1.     A  anterior,  B  posterior,   C  dorsal  view  (A  and  B  after  MIVART). 


1.  neural  spine. 

2.  neural  canal. 

3.  prezygapophysis. 

4.  postzygapophysis. 

5.  posterior  articular  surface  of 

centrum. 


6.  anterior  articular  surface  of 

centrum. 

7.  vertebrarterial  canal. 

8.  hypapophysis. 


332  THE  VERTEBRATE  SKELETON. 

VERTEBRAL  COLUMN. 

The  vertebral  column  of  birds  is  readily  divisible  into  a 
very  mobile  cervical  region,  and  an  extremely  rigid  post- 
cervical  region.  In  most  birds  the  vertebral  centra  are  with- 
out terminal  epiphyses,  but  these  structures  are  found  in 
Parrots.  The  cervical  vertebrae  are  generally  large  and  vary 
in  number  from  eight  or  nine  to  twenty -three  in  Swans. 
Except  in  some  extinct  forms,  such  as  Ichthyornis  and  Apa- 
tornis,  in  which  they  are  biconcave,  the  centra  are  charac- 
terised by  having  saddle-shaped  articulating  surfaces,  which 
in  front  are  concave  from  side  to  side  and  slightly  convex 
from  above  downwards,  while  posteriorly  they  are  convex 
from  side  to  side  and  concave  from  above  downwards.  The 
atlas  is  small  and  ring-like,  and  its  centrum  is  fused  with  the 
axis  forming  the  odontoid  process.  Cervical  ribs  are  often 
well  developed,  and  in  some  of  the  Ratitae  they  remain  for  a 
long  time  distinct  from  the  vertebrae. 

The  thoracic  vertebrae  are  distinguished  from  the  cervical 
by  the  fact  that  their  true  ribs  are  united  to  the  sternum 
by  means  of  sternal  ribs.  This  distinction,  however,  though 
convenient,  is  somewhat  arbitrary,  as  it  has  been  shown  that 
in  the  fowl  and  gannet,  two  pairs  of  ribs  which  in  the  adult 
are  free  from  the  sternum,  are  connected  with  it  in  the  em- 
bryo. When,  as  in  the  Swans,  the  thoracic  vertebrae  are 
not  all  fused  together,  they  generally  have  saddle-shaped 
articulating  surfaces,  but  sometimes,  as  in  the  Penguins,  Auks 
and  Plovers,  the  centra  are  convex  in  front  and  concave  be- 
hind. The  trunk  vertebrae  generally  have  well-marked  neural 
spines,  while  in  the  Divers  the  anterior  ones  have  peculiar 
bifurcating  hypapophyses. 

The  trunk  vertebrae  are  not  readily  divisible  into  thoracic 
and  lumbar.  There  are  two  true  sacral  -vertebrae,  but  as 
development  proceeds  a  number  of  other  vertebrae  become 
fused  with  the  true  sacrals,  the  whole  forming  a  large  com- 
pound sacrum.  These  pseudosacral  vertebrae  generally  include 


THE    SKELETON    IN    BIRDS.     THE    SKULL.  333 

the  lumbar,  and  some  of  the  thoracic  and  caudal  vertebrae. 
Sixteen  to  twenty  vertebrae  or  even  more  may  be  included 
in  the  compound  sacrum,  and  sometimes  the  whole  of  the 
trunk  vertebrae  are  fused  together.  In  Archaeopteryx  however 
but  five  vertebrae  take  part  in  the  formation  of  the  sacrum. 

In  Archaeopteryx  there  are  twenty  long  caudal  vertebrae, 
of  which  the  last  sixteen  carry  a  pair  of  feathers  apiece,  but 
in  all  other  birds  the  tail  is  short  and  in  the  great  majority 
of  cases  the  posterior  vertebrae  are  fused  together,  forming  the 
pygostyle.  In  the  Ratitae  and  Tinamidae  a  pygostyle  is  rarely 
or  imperfectly  developed.  In  Hesperornis  there  are  twelve 
caudal  vertebrae,  six  or  seven  of  which  are  united  by  their 
centra  only,  forming  an  imperfect  pygostyle. 

The  free  caudal  vertebrae  are  generally  amphicoelous. 

THE  SKULL. 

The  skull  of  all  birds  from  Archaeopteryx  onwards  is 
essentially  similar,  differing  from  the  skull  of  reptiles  mainly 
in  the  extent  to  which  the  cranium  is  arched,  and  its  greater 
size  in  proportion  to  the  jaws. 

Most  of  the  bones  of  the  cranium  are  pneumatic,  and  all 
show  a  marked  tendency  to  fuse  together,  and  have  their 
outlines  obliterated  by  the  disappearance  of  the  sutures.  The 
several  bones  remain  longest  distinguishable  in  the  Ratitae 
and  to  a  less  extent  in  the  Penguins.  The  orbits  are  very 
large  and  lie  almost  entirely  in  front  of  the  cranium ;  they 
are  separated  by  an  interorbital  septum  which  is  sometimes,  as 
in  Chauna  and  Scythrops,  very  complete,  sometimes,  as  in 
Hornbills  and  the  Common  Heron,  very  slightly  developed. 
As  a  general  rule  the  sclerotic  is  cartilaginous. 

The  anterior  nares  are  almost  always  situated  far  back 
at  the  base  of  the  beak  near  the  orbits,  but  in  Apteryx  they 
are  placed  right  at  its  extremity.  In  Phororhacos  they  are 
placed  very  high  up  on  the  enormous  beak  and  are  not  separ- 
ated by  any  bony  partition. 


334          THE  VERTEBRATE  SKELETON. 

The  skull  of  Parrots  has  some  peculiarities.  In  some 
Parrots  the  lachrymal  sends  back  a  process  which  meets  the 
postorbital  process  of  the  frontal  and  completes  the  orbit. 
In  most  birds  the  upper  beak  is  immovably  fixed,  but  in 
some  it  is  attached  to  the  cranium,  only  by  the  nasals  and 
by  flexible  processes  of  the  premaxillae,  so  that  by  this 
means  a  kind  of  elastic  joint  is  established  and  the  beak  is  able 
to  be  moved  on  the  cranium.  In  the  Parrots  and  Opisthocomus 
there  is  a  regular  highly  movable  joint. 

In  Cassowaries  the  fronto-nasal  region  of  the  skull  is  pro- 
duced into  an  enormous  bony  crest,  and  in  Hornbills  a 
somewhat  similar  structure  occurs.  Although  true  teeth  do 
not  occur  in  any  known  bird  except  Archaeopteryx,  Hesper- 
ornis,  and  Iclithyornis,  another  extinct  bird,  Odontopteryx,  has 
the  margins  of  both  jaws  provided  with  forwardly -directed 
tooth-like  serrations,  formed  of  part  of  the  actual  jawbone :  a 
living  hawk,  ffarpagus,  too,  has  a  deeply  notched  bill,  to 
which  correspond  serrations  in  the  premaxillae. 

A  basipterygoid  process  of  the  basisphenoid  abuts  against 
the  pterygoid  in  Ratitae  and  in  Tinamous,  plovers,  fowls, 
pigeons,  ducks  and  geese  among  Carinatae,  recalling  the 
arrangement  met  with  in  many  reptiles.  The  squamosal  is 
sometimes,  as  in  the  fowl,  united  with  the  postorbital  process 
of  the  frontal.  In  the  Carinatae  the  quadrate  articulates 
with  the  cranium  by  a  double  convex  surface,  in  the  Ratitae 
by  a  single  one.  The  premaxillae  are  always  comparatively 
large  bones,  the  maxillae  on  the  contrary  are  small,  but 
give  rise  to  important  inwardly-projecting  maxillo-palatine 
processes. 

The  relations  of  the  palatines,  pterygoids,  maxillae,  and 
vomers  vary  considerably,  and  on  them  Huxley  has  based  a 
classification  of  birds1.  In  the  Ratitae  and  the  Tinamous 
(Tinamidae),  among  Carinatae  the  vomers  unite  and  form  a 
large  broad  bone,  separating  the  palatines  and  the  pterygoids 
1  See  T.  H.  Huxley,  "On  the  Classification  of  Birds,"  P.  Z.  S.  1867. 


THE   SKELETON    IN    BIRDS.     THE    SKULL.  335 

from  the  rostrum.  Huxley  uses  the  term  Dromaeognathous 
to  describe  this  condition.  In  all  other  Carinatae  the  vomers 
are  narrow  behind,  and  the  palatines  and  pterygoids  converge 
posteriorly  and  articulate  largely  with  the  rostrum.  Three 
modifications  of  this  condition  are  distinguished  by  Huxley,  and 
termed  Schizognathous,  -flSgithognathous,  and  Desmo- 
gnathous. 

In  the  Schizognathae  the  vomers  coalesce  and  form  a 
narrow  elongated  bone,  pointed  in  front,  separating  the 
maxillo-palatine  processes  of  the  premaxillae.  Waders,  fowls, 
penguins,  gulls,  some  falcons  and  eagles,  American  vultures, 
some  herons  and  many  owls  have  the  Schizognathous  arrange- 
ment. In  pigeons  and  sandgrouse  there  is  no  vomer,  but  the 
other  bones  have  the  Schizognathous  arrangement. 

In  the  .flCgithognathae  the  arrangement  is  the  same  as  in 
the  Schizognathae,  except  that  the  vomers  are  truncated  in 
front.  Passeres,  swifts,  woodpeckers,  humming  birds,  rollers, 
hoopoes  have  this  arrangement. 

In  the  Desmognathae  (fig.  60,  A)  the  maxillo-palatine 
processes  approach  one  another  in  the  middle  line,  and  either 
unite  with  the  vomers,  or  unite  with  one  another,  hiding  the 
vomers.  Thus  a  more  or  less  complete  bony  roof  is  formed 
across  the  palate.  The  vomers  in  Desmognathae  are  small  or 
sometimes  absent.  Ducks,  storks,  most  herons,  most  birds  of 
prey  and  owls,  pelicans,  cormorants,  parrots,  and  flamingoes 
are  Desmognathous. 

The  mandible,  as  in  other  Sauropsids,  consists  of  a  cartilage 
bone,  the  articular,  and  a  series  of  membrane  bones,  the 
dentary,  splenial,  coronoid,  angular,  and  supra-angular,  de- 
veloped round  the  unossified  Meckel's  cartilage.  The  dentaries 
of  the  two  rami  are  nearly  always  fused  together,  but  in 
Ichthyornis  and  Archaeopteryx  the  two  rami  are  but  loosely 
united.  There  is  often  a  fontanelle  between  the  dentary  and 
the  posterior  bones,  while  the  angle  is  sometimes,  as  in  the 
fowl,  drawn  out  into  a  long  curved  process. 


336          THE  VERTEBRATE  SKELETON. 

The  hyoid  apparatus  (fig.  59,  C)  consists  of  a  median 
portion,  and  a  pair  of  cornua.  The  median  portion  is  com- 
posed of  three  pieces  placed  end  to  end,  and  called  respectively 
the  os  entoglossum,  the  basi-hyal,  and  the  uro-hyal.  The  os 
entoglossum  is  shown  by  development  to  be  formed  by  the 
union  of  paired  structures  and  is  probably  homologous  with  the 
hyoid  arch  of  fishes.  The  basihyal  and  the  long  cornua,  each 
of  which  is  composed  of  two  or  three  pieces  placed  end  to  end, 
are  homologous  with  the  first  branchial  arch  of  fishes,  while 
the  urohyal  is  probably  homologous  with  the  second  branchial 
arch  of  fishes.  In  Woodpeckers  the  cornua  are  enormously 
long,  and  curve  over  the  skull,  extending  as  far  forwards  as 
the  anterior  nares. 

RIBS  AND  STERNUM. 

Well-developed  ribs  are  attached  to  the  posterior  cervical 
vertebrae  as  well  as  to  the  thoracic  vertebrae.  The  ribs 
generally  have  uncinate  processes  and  separate  capitula  and 
tubercula,  but  uncinate  processes  are  absent  in  Chauna  Pala- 
medea  and  apparently  in  Archaeopteryx. 

The  sternum  (fig.  63)  is  greatly  developed  in  all  birds.  In 
the  embryo1  it  is  seen  to  be  derived  from  the  union  of  right 
and  left  plates  of  cartilage,  formed  by  the  fusion  of  the  ventral 
ends  of  the  ribs.  In  the  Ratitae  and  a  few  Carinatae,  such 
as  Stringops,  it  is  flat,  but  in  the  great  majority  of  birds 
it  is  keeled,  though  the  development  of  the  keel  varies  greatly. 
It  is  large  in  the  flightless  Penguins,  which  use  their  wings 
for  swimming.  Traces  of  an  interclavicle  may  occur  in  the 
embryo. 

PECTORAL  GIRDLE. 

The   pectoral   girdle   is    also    strongly    developed    in    all 

Carinatae,  but  is  much  reduced  in  Ratitae.     In  some  Moas 

the  sternum  has  no  facet  for  the  articulation  of  the  coracoid, 

and  the  pectoral  girdle  appears  to  have  been  entirely  absent ; 

1  B.  Lindsay,  P.  Z.  S.  1885,  p.  684. 


THE   SKELETON    IN    BIRDS.      THE    PECTORAL   GIRDLE.     337 


FIG.  63.     SHOULDER-GIRDLE  AND  STERNUM  OF 

A.  BLACK  VULTURE  (Vultur  cinereus)x%. 

B.  PEACOCK  (Pavo  cristatus)  x  f . 

C.  PELICAN  (Pelicanus  conspic Hiatus)  x  ^.     (All  Camb.  Mus.) 

1.  carina  of  the  sternum.  6.     surfaces  for  articulation  with 

2.  coracoid.  the  sternal  ribs. 

3.  scapula.  7.     xiphoid  processes. 

4.  clavicle.  8.     fontanelle. 

5.  costal  process. 

R.  22 


338          THE  VERTEBRATE  SKELETON. 

it  is  extremely  small  also  in  Apteryx.  Clavicles  are  generally 
well  developed  in  the  Carinatae,  and  small  ones  are  found 
also  in  Hesperornis,  and  in  Emeus  and  Cassowaries.  In  the 
other  living  Ratitae  and  in  Stringops  they  are  absent.  In 
some  Parrots,  Owls  and  Toucans  they  do  not  meet  one  another 
ventrally.  Clavicles  are  especially  stout  in  some  of  the  birds 
of  prey.  They  do  not  generally  touch  the  sternum,  but  some- 
times, as  in  the  Pelican  (fig.  63,  C),  Adjutant  and  Frigate  bird, 
they  are  fused  with  it. 

In  all  Ratitae  the  scapula  and  coracoid  lie  almost  in  the 
same  straight  line  with  one  another,  in  the  Carinatae  they  are 
nearly  at  right  angles  to  one  another. 

ANTERIOR  LIMB. 

In  the  wing  of  nearly  all  birds  the  ulna  is  thicker  than  the 
radius,  but  in  Arcliaeopteryx  the  two  bones  are  equal  in  size. 
In  the  wing  of  Archaeopteryx  there  are  three  long  digits  with 
distinct  metacarpals.  In  all  other  birds  the  digits  are  modi- 
fied, the  metacarpals  being  commonly  fused  and  the  phalanges 
reduced  in  number.  In  Palamedea  and  some  other  birds  the 
metacarpus  bears  a  bony  outgrowth,  which  when  sheathed  in 
horn  forms  a  spur. 

In  most  of  the  Ratitae  and  in  the  extinct  Dodo  (Didus) 
and  Solitaire  (Pezophaps}  the  wing  is  very  small,  but  the 
.usual  parts  are  recognisable.  In  Hesperornis  apparently  only 
the  humerus  is  present ;  in  some  Moas,  in  which  the  wing  is 
imperfectly  known,  the  presence  of  the  humerus  is  indicated 
by  traces  of  a  glenoid  cavity.  In  most  Moas  the  wing  is 
apparently  completely  absent.  As  compared  with  those  in  other 
Ratitae,  the  wings  of  the  Ostrich  and  Rhea  are  well  developed. 
In  the  Ostrich  (fig.  64,  B)  and  Rhea,  as  in  nearly  all  Carinatae, 
the  manus  has  three  digits,  but  in  Apteryx  there  is  only  a  single 
digit,  the  second.  The  Penguins  (fig.  64,  A)  too  among  Cari- 
natae have  only  two  digits,  but  in  their  case  it  is  the  pollex 
which  is  missing.  In  the  Ostrich  the  third  digit  has  two 
phalanges,  in  all  other  living  birds  it  has  only  one  phalanx. 


THE    SKELETON    IN    BIRDS.      THE    PELVIC    GIRDLE.      339 


PELVIC  GIRDLE. 

Birds  have  a  very  large    pelvis    and     its   characters   are 
constant   throughout   almost    the    whole    group.      The   ilium 


FIG.  64.     BONES  OF  THE  EIGHT  WING  OF 

A.  A  PENGUIN  x  ^.     (Camb.  Mus.) 

B.  OSTRICH  (Stnithio  camelw)x±.    (Partly  after  PARKER.) 

C.  GANNET  (Sula  alba)  x  ^.     (Camb.  Mus.) 

In  C  the  distal  phalanges  of  the  pollex  and  second  digit  have  been 
omitted. 
1.     humerus.  6.     pollex. 

radius.  7.     second  digit, 

ulna.  8.     cuneiform, 

second  metacarpal.  9.     sesamoid  bone, 

third  metacarpal. 


is  very  large,  and  is  united  along  its  whole  length  with 
the  sacral  and  pseudosacral  vertebrae.  The  ischiurn  is  broad 
and  extends  back  parallel  to  the  ilium  with  which  in  most 

22—2 


340 


THE  VERTEBRATE  SKELETON. 


FIG.  65.     PELVIC  GIKDLE  AND  SACRUM  OF 

A.  CASSOWARY  (Casuarius  galeatus)  x  £. 

B.  OWEN'S  APTERYX  (A.  oweni)x%. 

C.  BROAD  BILLED  RHEA  (B.  macrorhyncha)  x  £. 

D.  OSTRICH  (Struthio  camelus)  x  TV.     (All  Camb.  Mus.) 


1.  ilium. 

2.  ischium. 

3.  pubis. 


4.  acetabulum. 

5.  pectineal  process. 


THE   SKELETON    IN    BIRDS.      THE    PELVIC    GIRDLE.      341 

birds  it  fuses  posteriorly,  further  forward  the  ilio-sciatic 
foramen  separates  the  two  bones.  In  Tinamus,  Hesperornis, 
Apteryx  (fig.  65,  B,  2),  and  Struthio,  the  ischia  are  separate 
from  the  ilia  along  their  whole  length  except  at  the  acetabu- 
lum ;  in  Phororhacos,  on  the  other  hand,  the  two  bones  are 
fused  along  almost  their  whole  length.  The  bone  usually 
called  the  pubis  in  birds  corresponds  to  the  post-pubis  of 
Dinosaurs  and  forms  a  long  slender  rod  (fig.  65,  3)  lying 
parallel  to  the  ischiurn.  In  many  birds  the  ischia  and  pubes 
are  united  at  their  distal  ends.  This  is  the  case  in  the  Ostrich 
(fig.  65,  D),  in  which  the  ilia  and  ischia  are  widely  separated. 
In  many  birds  the  pubis  is  drawn  out  in  front  into  the  pectineal 
process,  this  is  specially  large  in  Apteryx  (fig.  65,  B,  5),  and  in 
the  embryos  of  many  birds.  It  is  probably  homologous  with  the 
pre-pubis  of  Dinosaurs  but  in  some  birds  is  formed  in  part  by 
the  ilium.  The  acetabulum  in  birds  is  always  perforate. 

In  Rhea  (fig.  65,  C,  2)  and  probably  in  Archaeopteryx  a 
symphysis  ischii  occurs,  and  in  the  ostrich  alone  among  birds 
there  is  a  symphysis  pubis.  In  Archaeopteryx  all  three  bones 
of  the  pelvis  are  distinct,  but  they  are  imperfectly  known.  In 
Ichthyornis  they  are  also  distinct,  in  all  other  known  birds 
they  are  fused  together  to  a  greater  or  less  extent. 

POSTERIOR  LIMB. 

The  tibia  is  always  well  developed  and  has  a  very  strong 
cnemial  crest.  The  proximal  tarsals  are  fused  with  its 
distal  end,  the  whole  forming  a  compound  bone,  the  tibio- 
tarsus.  There  is  frequently  an  oblique  bar  of  bone  crossing 
the  anterior  face  of  the  tibio-tarsus  at  the  distal  end,  just 
above  the  articular  surface  of  the  tarso-metatarsus,  this  is 
absent  in  Ostriches  and  sEpyornis.  The  fibula  though  in  the 
embryo  and  in  Archaeopteryx  equal  in  length  to  the  tibia,  is  in 
the  adult  of  other  birds  always  imperfect,  its  proximal  end 
is  often  fused  with  the  tibia,  and  its  distal  end  is  commonly 
atrophied.  In  the  Penguins  however  the  distal  end  is  com- 
plete. The  distal  tarsals  fuse  with  the  second,  third  and  fourth 


342  THE  VERTEBRATE  SKELETON. 

metatarsals,  forming  a  compound  bone,  the  tarso-metatarsus. 
The  first  metatarsal  is  nearly  always  free  but  occasionally 
as  in  Phaethon  it  is  fused  with  the  others.  No  adult  bird 
has  more  than  four  digits  in  the  pes.  In  the  Penguins  the 
metatarsals  are  separate,  and  in  many  birds  larger  or  smaller 
gaps  exist  between  the  fused  metatarsals.  In  most  birds 
the  third  metatarsal  is  curved  so  as  not  to  lie  in  the  same 
plane  as  the  others,  but  in  the  Penguins  they  all  three  lie  in 
the  same  plane.  The  metatarsals  are  clearly  separated  in 
Archaeopteryx.  In  Gallinaceous  birds  the  tarso-metatarsus 
bears  a  bony  outgrowth  which  is  sheathed  in  horn  and  forms 
a  spur. 

In  most  birds  the  first  four  toes  are  present  while  the  fifth 
is  always  absent.  The  first  toe  commonly  has  two  phalanges, 
the  second  three,  the  third  four,  and  the  fourth  five.  In 
Swifts  the  third  and  fourth  toes  have  only  three  phalanges. 
Many  birds,  such  as  all  Ratitae  except  Apteryx,  have  only  three 
toes,  the  hallux  being  absent ;  in  the  Ostrich  the  second  toe  is 
also  gone  with  the  exception  of  a  small  metatarsal,  so  that  the 
foot  retains  only  the  third  and  fourth  digits,  the  third  being 
much  the  larger  of  the  two  and  bearing  a  claw,  while  the 
fourth  is  clawless. 

In  the  Swifts,  Cormorants,  and  Penguins,  all  four  toes  are 
directed  forwards.  In  most  birds  the  hallux  is  directed  back- 
wards, and  the  other  toes  forwards.  In  the  Owls  the  fourth 
toe  can  be  directed  backwards  as  well  as  the  hallux,  while 
in  Parrots,  Cuckoos,  Woodpeckers,  and  Toucans  the  fourth  toe 
is  permanently  reversed.  In  Trogons  the  second  toe  is  reversed 
in  addition  to  the  hallux,  but  not  the  fourth. 


CHAPTER   XX. 

CLASS   MAMMALIA. 

THE  skeleton  of  the  members  of  this  class,  the  highest  of 
the  vertebrata,  has  the  following  characteristics  : — 

Some  part  of  the  integument  at  some  period  of  life  is 
always  provided  with  hairs;  these  are  epidermal  structures 
arising  from  short  papillae  of  the  Malpighiaii  layer  of  the 
epidermis,  which  at  once  grow  inwards  and  become  imbedded 
in  pits  of  the  dermis.  Sometimes  scales  or  spines  occur,  and 
epidermal  exoskeletal  structures  in  the  form  of  hoofs,  nails, 
claws  and  horns  are  also  characteristic.  As  regards  the  endo- 
skeleton,  the  vertebral  centra  have  terminal  epiphyses  except 
in  the  Ornithodelphia  and  some  Sirenia.  In  the  skull  the 
cranial  region  is  greatly  developed  as  compared  with  that  in 
lower  vertebrates,  and  whereas  in  many  reptiles  the  true 
cranium  is  largely  concealed  by  a  false  roof,  in  mammals  the 
only  relic  of  this  secondary  roof  is  found  in  the  zygomatic 
arch,  and  postorbital  bar.  In  the  adult  all  the  bones  except 
the  mandible,  hyoid,  and  auditory  ossicles  are  firmly  united 
together.  The  basisphenoid  is  well  ossified,  and  there  is  no 
parasphenoid.  The  pro-otic  ossifies,  and  unites  with  the  epi-otic 
and  opisthotic  before  they  coalesce  with  any  other  bones. 

The  skull  articulates  with  the  vertebral  column  by  means 
of  two  convex  occipital  condyles  formed  mainly  by  the  ex- 
occipitalsr  and  the  mandible  articulates  with  the  squamosal 
without  the  intervention  of  the  quadrate.  The  latter  is  much 
reduced,  and  is  converted  into  the  tympanic  ring,  while  the 
hyomandibular  of  fish  is  represented  by  the  auditory  ossicles1. 
1  This  is  Gadow's  view ;  according  to  Huxley  the  quadrate  forms  the 


344  THE  VERTEBRATE  SKELETON. 

The  teeth  are  always  attached  to  the  maxillae,  premaxillae 
and  mandibles,  never  to  any  of  the  other  bones.  They  are 
nearly  always  implanted  in  distinct  sockets,  and  are  hardly  ever 
ankylosed  to  the  bone.  The  teeth  of  mammals  are  generally 
markedly  heterodont,  four  forms,  incisors,  canines,  premolars, 
and  molars,  being  commonly  distinguishable.  Some  mammals 
are  monophyodont,  having  only  a  single  set  of  teeth,  but  the 
great  majority  are  diphyodont,  having  two  sets,  a  deciduous  or 
milk  dentition,  and  a  permanent  dentition. 

The  incisors,  the  front  teeth,  are  simple,  one-rooted,  adapted 
for  cutting,  and  are  nearly  always  borne  by  the  premaxillae. 
Next  come  the  canines,  one  on  each  side  in  each  jaw.  They  are 
generally  large  teeth  adapted  for  tearing  or  holding,  and  get 
their  name  from  the  fact  that  they  are  largely  developed  in  the 
dog.  The  remaining  teeth  form  the  grinding  series,  the  more 
posterior  of  them,  being  the  molars,  which  are  not  preceded  by 
milk  teeth '.  Between  the  molars  and  the  canines  are  the  pre- 
molars, which  do  as  a  rule  have  milk  or  deciduous  predecessors, 
though  very  frequently  the  first  of  them  is  without  a  milk 
predecessor. 

In  describing  the  dentition  of  any  mammal,  for  the  sake  of 
brevity  a  formula  is  generally  made  use  of.     Thus,  the  typical 
mammalian  dentition  is  expressed  by  the  formula 
.31          4        3      11 
*3CT^4m<ril' 

giving  twenty-two  teeth  011  each  side,  or  forty-four  altogether2. 
The  incisors  are  represented  by  i,  the  canines  by  c,  the  pre- 
molars by  p  or  pm,  and  the  molars  by  m.  The  numbers  above 
the  lines  represent  the  teeth  in  the  upper  jaw,  those  below 

malleus ;  according  to  Baur  it  forms  the  zygomatic  process  of  the  squa- 
mosal,  and  according  to  Broom  the  interarticular  mandibular  cartilage. 

1  According  to  Leche,  MorphoL  Jahrb.  xix.  p.  502,  the  molar  teeth 
belong  morphologically  to  the  first  series,  i.e.  they  are  milk  teeth  without 
vertical  successors. 

2  The  researches  of  Bateson,  P.  Z.  S.  1892,  p.  102,  have  shown  that 
cases  of  individual  variation  in  the  number  of  teeth  are  common. 


MAMMALIA.  345 

the  lines  the  teeth  in  the  lower  jaw.  The  milk  dentition  is 
expressed  by  a  similar  formula  with  d  (deciduous)  prefixed  to 
the  letter  expressing  the  nature  of  the  tooth. 

The  following  terms  are  of  frequent  use  as  characterising 
certain  forms  of  the  grinding  surfaces  of  teeth,  and  it  will  be 
well  to  define  them  at  once. 

Bunodont  is  a  term  applied  to  teeth  with  broad  crowns 
raised  into  rounded  tubercles,  e.g.  the  grinding  teeth  of  Pigs 
and  Hippopotami ; 

Bilophodont  to  teeth  marked  by  a  simple  pair  of  trans- 
verse ridges,  with  or  without  a  third  ridge  running  along  the 
outer  border  of  the  tooth  at  right  angles  to  the  other  two, 
e.g.  the  grinding  teeth  of  Lopkiodon,  Kangaroo,  Manatee, 
Tapir,  Dinotheriu7n ; 

Selenodont  to  teeth  marked  by  crescentic  ridges  running 
from  the  anterior  towards  the  posterior  end  of  the  tooth,  e.g. 
the  grinding  teeth  of  the  Ox  and  Sheep. 

Teeth  whose  crowns  are  low  so  that  their  whole  structure 
is  visible  from  the  grinding  surface  are  called  brachydont,  while 
those  with  higher  crowns,  in  which  the  bases  of  the  infoldings 
of  enamel  are  invisible  from  the  grinding  surface  are  said  to 
be  hypsodont.  Bunodont  teeth  are  brachydont,  the  teeth  of  the 
Horse  and  Ox  are  hypsodont. 

Passing  now  to  the  appendicular  skeleton — the  shoulder 
girdle  differs  markedly  from  that  of  Sauropsids  in  the  fact  that 
the  coracoid,  except  in  the  Ornithodelphia,  is  greatly  reduced, 
generally  forming  only  a  small  process  on  the  scapula.  In  the 
pelvis  the  pubes  meet  in  a  ventral  symphysis,  except  in  some 
Insectivora  and  Chiroptera.  In  many  mammals  a  fourth  pelvic 
element,  the  acetabular  bone,  is  distinguishable.  The  ankle 
joint  is  cruro-tarsal,  or  situated  between  the  proximal  tarsal 
bones  and  the  tibia  and  fibula.  Carpalia  4  and  5  are  united 
forming  the  unciform ;  and  the  ulnar  sesamoid  bone  or  pisiform 
is  generally  well  developed.  In  the  proximal  row  of  tarsal  ele- 
ments there  are  only  two  bones,  the  calcaneum  and  astragalus. 


346          THE  VERTEBRATE  SKELETON. 

Of  these  the  calcaneum  is  the  fibulare,  and  the  astragalus  is 
generally  regarded  as  the  tibiale  and  intermedium  fused1. 

Subclass  I.     ORNITHODELPHIA  OR  PROTOTHERIA. 

This  sub-class  contains  only  a  single  order,  the  Monotre- 
mata,  and  the  following  characteristics  are  equally  applicable 
to  the  subclass  and  to  the  order.  The  vertebral  centra  have 
no  epiphyses,  and  the  odontoid  process  remains  for  a  long  time 
free  from  the  centrum  of  the  second  vertebra.  With  the 
exception  of  the  atlas  of  Echidna  the  cervical  vertebrae  are 
without  zygapophyses.  The  cranial  walls  are  smooth  and 
rounded,  and  the  sutures  between  the  several  bones  early 
become  completely  obliterated  as  in  birds.  The  mandible  is  a 
very  slight  structure,  with  no  ascending  ramus,  and  with  the 
coronoid  process  (see  p.  398)  and  angle  rudimentary.  The 
auditory  ossicles  show  a  low  state  of  development.  The  tuber- 
cula  of  the  ribs  articulate  with  the  sides  of  the  centra  of  the 
thoracic  vertebrae,  not  with  the  transverse  processes.  Some  of 
the  cervical  ribs  remain  for  a  long  time  separate  from  the  verte- 
brae. Well  ossified  sternal  ribs  occur.  No  true  teeth  are  present 
in  the  adult.  The  young  Ornithorhynchus  has  functional  molar 
teeth,  but  in  the  adult  their  place  is  taken  by  horny  plates. 
In  the  Echidnidae  neither  teeth  nor  horny  plates  occur. 

The  coracoid  (fig.  66,  3)  is  complete  and  well  developed, 
and  articulates  with  the  sternum.  A  precoracoid  (epicoracoid) 
occurs  in  front  of  the  coracoid,  and  there  is  a  large  interclavicle 
(fig.  66,  6).  The  ridge  on  the  scapula,  corresponding  to  the 
spine  of  other  mammals,  is  situated  on  the  anterior  border 
instead  of  in  the  middle  of  the  outer  surface.  Epipubic  bones 
are  present.  In  the  Echidnidae,  but  not  in  Ornithorkynchus*, 

1  Baur,  however,  suggests  (Anat.   Anz.  vol.  iv.  1889),  that  a  tibial 
sesamoid  found  in  Procavia,  many  rodents,  edentates  and  Ornithorhyn- 
chus is  a  vestigial  tibiale,  and  that  the  astragalus  is  the  intermedium. 

2  This  perforation  of  the  acetabulum   in   Echidna   is   a   secondary 
character  occurring  late  in  development,   and  consequently  is  not   of 
phylogenetic  importance. 


MAMMALIA.      ORNITHODELPHIA. 


347 


the  central  portion  of  the  acetabulum  is  unossified  as  in  birds. 
The  humerus  has  a  prominent  deltoid  crest ;  its  ends  are  much 
expanded,  and  the  distal  end  is  pierced  by  an  ent-epicondylar 


FIG.  66.     VENTRAL  VIEW  OF  THE  SHOULDER-GIRDLE  AND  STERNUM  OF 
A  DUCKBILL  (Ornithorhynchus  paradoxus)  x  f  (after  PARKER). 

1  and  2.     scapula.  8.  presternum. 

3.  coracoid.  9.  third    segment    of    mesoster- 

4.  precoracoid  (epicoracoid).  num. 

5.  glenoid  cavity.  10.  sternal  rib. 

6.  interclavicle.  11.  intermediate  rib. 

7.  clavicle.  12.  vertebral  rib. 

foramen.  The  fibula  has  a  broad  proximal  process  resembling 
an  olecranon.  The  limbs  and  their  girdles  bear  a  striking 
resemblance  to  those  of  some  Theromorphous  reptiles. 

The  order  Monotremata  includes  only  two  living  families, 
the  Echidnidae  and  Ornithorhynchidae. 


348  THE   VERTEBRATE    SKELETON. 


MAMMALIA1. 

It  will  be  well  here  to  briefly  refer  to  certain  mammals 
of  small  size,  the  remains  of  which  have  been  found  in  de- 
posits of  Mesozoic  age.  In  the  great  majority  of  cases  they 
are  known  only  by  the  lower  jaw,  or  sometimes  only  by  isolated 
teeth.  A  large  number  of  them  are  commonly  grouped 
together  as  the  Multituberculata,  and  are  sometimes,  partly 
owing  to  the  resemblance  of  their  teeth  to  those  of  Ornitho- 
rhynchus,  placed  with  the  Prototheria,  sometimes  between  the 
Prototheria  and  the  Metatheria.  They  are  characterised  by 
having  a  single  pair  of  large  incisors  in  the  lower  jaw,  and  one 
large  with  one  or  two  smaller  incisors  in  each  .  premaxilla. 
The  lower  canines  are  very  small  or  altogether  wanting.  The 
incisors  are  separated  by  a  diastema  from  the  grinding  teeth, 
which  are  sometimes  (Tritylodon)  characterised  by  the  posses- 
sion of  longitudinal  rows  of  little  tubercles  separated  by 
grooves,  sometimes  by  having  the  premolars  provided  with 
high  cutting  edges,  whose  surfaces  are  obliquely  grooved. 
Some  of  the  Mesozoic  mammals  found  associated  with  the 
Multituberculata,  have  however  a  dentition  of  an  altogether 
different  type,  with  at  least  three  lower  incisors,  well  developed 
canines  and  premolars,  and  numerous  molars  with  peculiar 
three-cusped  or  tritubercular  grinding  surfaces.  These  mam- 
mals, one  of  the  best  known  of  which  is  Phascolotherium,  are 
commonly  separated  from  the  Multituberculata,  and  are  divided 
by  Osborn  into  two  groups,  one  allied  to  the  Marsupials,  and 
one  to  the  Insectivores.  The  group  showing  Marsupial  affinities 
is  further  subdivided  into  carnivorous,  omnivorous,  and  herbi- 
vorous subgroups.  The  members  of  both  groups  commonly 

1  See  K.  Owen,  "Monograph  of  the  Fossil  Mammalia  of  the  Mesozoic 
Formation,"  Pal.  Soc.  Hon.  1871. 

H.  F.  Osborn,  "Structure  and  Affinities  of  Mesozoic  Mammals," 
J.  ofPhilad.  Acad.  1888,  vol.  ix. 

O.  C.  Marsh,  "Jurassic  Mammals,"  Amer.  J.  Sci.  1878  et  seq. 


MAMMALIA.      DIDELPHIA.  349 

have  four  premolars,  and  six  to  eight  molars  in  each  mandibular 
ramus. 

Subclass  IL     DIDELPHIA  OR  METATHERIA. 

This  subclass,  like  the  previous  one,  contains  only  a  single 
order,  viz.  the  Marsupialia1;  but  the  forms  referable  to  it  are 
far  more  numerous  than  in  the  case  of  the  Monotremata. 

The  integument  is  always  furry,  and  the  teeth  are  always 
differentiated  into  incisors,  canines,  premolars  and  molars. 
Except  in  Phascolomys,  the  number  of  incisors  in  the  upper 
and  lower  jaws  is  never  equal,  and  the  number  in  the  upper 
usually  exceeds  that  in  the  lower  jaw.  There  is  no  such 
regular  succession  and  displacement  of  teeth  as  in  most  mam- 
mals. Sometimes  the  anterior  teeth  are  diphyoclont,  and  as  a 
general  rule  the  tooth  commonly  regarded  as  the  last  premolar 
is  preceded  by  a  milk  tooth.  The  majority  of  the  permanent 
teeth  of  most  Marsupials  are  regarded  as  belonging  to  the  milk 
series  for  two  reasons,  (1)  they  are  developed  from  the  more 
superficial  tissues  of  the  jaws,  (2)  a  second  set,  the  permanent 
teeth,  begin  to  develop  as  outgrowths  from  them,  but  after 
wards  become  aborted2. 

The  odontoid  process  at  an  early  stage  becomes  fused  with 
the  centrum  of  the  second  cervical  vertebra,  and  the  number 
of  thoraco-lumbar  vertebrae  is  always  nineteen.  The  skull  has 
several  characteristic  features.  The  tympanic  bone  remains 
permanently  distinct,  and  the  anterior  boundary  of  the  tym- 
panic cavity  is  formed  by  the  alisphenoid.  The  carotid  canal 
perforates  the  basisphenoid,  and  the  lachrymal  canal  opens 
either  outside  the  orbit  or  at  its  margin.  There  are  generally 
large  vacuities  in  the  palate.  The  angle  of  the  mandible  is 
(except  in  Tarsipes)  more  or  less  inflected  ;  and  as  a  rule  the 
jugal  furnishes  part  of  the  articular  surface  for  the  mandible. 

1  See  Oldfield  Thomas,  Brit.  Mus.  Cat.  of  Marsupialia  and  Monotre- 
mata (1888). 

2  W.  Kiikenthal,  Anat.  Anz.  vi.  p.  364,  1891.     C.  Rose,  Anat.  Anz. 
vn.  p.  639. 


350          THE  VERTEBRATE  SKELETON. 

There  is  no  precoracoid  (epicoracoid)  or  interclavicle,  and  the 
coracoid  is  reduced  to  form  a  mere  process  of  the  scapula,  not 
coming  near  the  sternum. 

Epipubic,  or  so-called  marsupial  bones1,  nearly  always 
occur,  and  a  fourth  pelvic  element,  the  acetabular  bone,  is 
frequently  developed.  The  fibula  is  always  complete  at  its 
distal  end,  sometimes  it  is  fused  with  the  tibia,  but  often  it  is 
not  only  free  but  is  capable  of  a  rotatory  movement  on  the 
tibia.  This  is  the  case  in  the  families  Phascolomyidae,  Didel- 
phyidae,  and  Phalangeridae. 

The  Marsupialia  can  be  subdivided  into  two  main  groups, 
according  to  the  character  of  the  teeth  : — 

1.  POLYPROTODONTIA. 

In  this  group  the  incisors  are  small,  subequal  and  nume- 
rous, not  less  than  ±.  The  canines  are  larger  than  the 
incisors,  and  the  molars  have  sharp  cusps.  The  members  of 
this  group  are  all  more  or  less  carnivorous  or  insectivorous. 
The  group  includes  the  families  Didelphyidae,  Dasyuridae, 
Peramelidae,  and  Notary  ctidaea. 

2.  DlPROTODONTIA. 

In  this  group  the  incisors  do  not  exceed  §,  and  are  usually 
f ,  occasionally  i.  The  first  upper  and  lower  incisors  are  large 
and  cutting.  The  lower  canines  are  always  small  or  absent, 
and  so  in  most  cases  are  the  upper  canines.  The  molars  have 
bluntly  tuberculated,  or  transversely  ridged  crowns.  The 
group  includes  the  families  Phascolomyidae,  Phalangeridae, 
Macropodidae,  and  Epanorthidae. 

1  These  bones  however  have  no  connection  with  the  marsupium, 
being  nearly  equally  developed  in   both  male   and  female.     They  are 
simply  sesamoid  bones  forming  ossifications  in  the.  inner  tendon  of  the 
external  oblique  muscle,  and  are  developed  as  supports  for  the  abdominal 
wall.     Very  similar  structures  have   been   independently  developed  in 
various  Amphibians,  Reptiles  and  monodelphian  Mammals.  See  W.  Leche, 
Biol.  Foren.  in.  p.  120. 

2  See  H.  Gadow,  P.  Z.  S.  1892,  p.  361. 


MAMMALIA.       EDENTATA.  351 

Subclass    III.       MONODELPHIA    OR    EUTHERIA. 

This  great  group  includes  all  the  Mammalia  except  the 
orders  Monotremata  and  Marsupialia.  Coming  to  their 
general  characteristics — as  in  the  Didelphia  the  odontoid 
process  and  cervical  ribs  early  become  fused  with  the  centra 
which  bear  them,  while  the  coracoid  is  reduced  so  as  to  form  a 
mere  process  on  the  scapula,  and  there  is  no  precoracoid  (epi- 
coracoid),  such  as  is  found  in  Ornithodelphia.  Clavicles  may 
be  present  or  absent ;  when  fully  developed  they  articulate 
with  the  sternum,  usually  directly,  but  occasionally,  as  in  some 
Rodents  and  Insectivores,  through  the  remains  of  the  sternal 
end  of  the  precoracoid.  There  is  never  any  interclavicle  in 
the  adult,  though  sometimes  traces  of  it  occur  during  develop- 
ment. In  the  pelvis  the  acetahula  are  imperforatc ;  and  well- 
developed  epipubic  bones  are  never  found  in  the  adult, 
though  traces  of  them  occur  in  some  Carnivores  and  foetal 
Ungulates. 

Order  1.     EDENTATA  '. 

Teeth  are  not,  as  the  name  of  the  order  seems  to  imply, 
always  wanting;  and  sometimes  they  are  very  numerous. 
They  are,  however,  always  imperfect,  and,  with  very  few 
exceptions,  are  homodont  and  monophyodont.  They  have 
persistent  pulps,  and  so  grow  indefinitely  and  are  never  rooted. 
In  all  living  forms  they  are  without  enamel,  consisting  merely 
of  dentine  and  cement,  and  are  never  found  in  the  front  part  of 
the  mouth  in  the  situation  occupied  by  the  incisors  of  other 
mammals.  These  characters  derived  from  the  teeth  are  the 
only  ones  common  to  the  various  members  of  the  order, 

1  See  W.  H.  Flower,  "On  the  Mutual  Affinities  of  the  Animals  com- 
posing the  order  Edentata,"  P.  Z.  S.  1882,  p.  358.  For  the  fossil 
Edentates  of  N.  America  see  E.  Cope,  Amer.  Natural.  1889;  for  those  of 
S.  America  see  various  papers  by  F.  Ameghino,  H.  Burmeister  and  E. 
Owen.  Also  T.  H.  Huxley,  "On  the  Osteology  of  Glyptodon,"  Phil. 
Trans.  1865. 


352  THE  VERTEBRATE  SKELETON. 

which  includes  the  living  sloths,  anteaters,  armadillos,  pangolins 
and  aard  varks,  together  with  various  extinct  forms,  chiefly 
found  in  beds  of  late  tertiary  age  in  both  North  and  South 
America,  the  best  known  being  the  Megatheridae  and  Glypto- 
donts. 

Order  2.     SiRENiA1. 

The  skeleton  of  these  animals  has  a  general  fish-like  form, 
in  correlation  with  their  purely  aquatic  habits.  The  fore  limbs 
have  the  form  of  paddles,  but  the  number  of  phalanges  is  not 
increased  beyond  the  normal.  There  are  no  external  traces  of 
hind  limbs. 

The  whole  skeleton  and  especially  the  skull  and  ribs  is 
remarkably  massive  and  heavy.  The  dentition  varies ;  in  the 
two  living  genera  Manatus  and  Halicore,  incisor  and  molar 
teeth  are  present,  in  one  extinct  genus,  Rhytina,  teeth  are 
entirely  absent,  while  in  another,  Halitherium^  the  dentition 
is  more  decidedly  heterodont  than  in  living  forms.  In  the 
two  living  genera  the  dentition  is  monophyodont,  but  in 
Halitherium  the  anterior  grinding  teeth  are  preceded  by 
milk  teeth.  The  tongue  and  anterior  part  of  the  palate  and 
lower  jaw  are  covered  with  roughened  horny  plates.  The 
skull  is  noticeable  for  the  size  and  backward  position  of  the 
anterior  nares,  also  for  the  absence  or  small  size  of  the  nasal 
bones.  There  is  no  union  of  certain  of  the  vertebrae  to  form 
a  sacrum,  and  in  living  forms  the  centra  are  not  terminated  by 
well-formed  epiphyses2. 

The  cervical  vertebrae  are  much  compressed,  but  they  are 
never  ankylosed  together.  In  Manatus  there  are  only  six 
cervical  vertebrae.  The  caudal  vertebrae  have  well-developed 
chevron  bones.  The  humerus  is  distinctly  articulated  to  the 

1  See  J.  F.  Brandt,  Symbolae  Sirenologicae,  St  Petersburg,  1846,  1861, 
1868. 

2  Epiphyses  are  fully  developed  in  Halitherium,  and  traces  occur  in 
Manatus. 


MAMMALIA.      CETACEA.  353 

radius  and  ulna,  and  these  two  bones  are  about  equally  de- 
veloped, and  are  often  fused  together.  There  are  no  clavicles, 
and  the  pelvis  is  vestigial,  consisting  of  a  pair  of  somewhat 
cylindrical  bones  suspended  at  some  distance  from  the  ver- 
tebral column.  In  living  forms  there  is  no  trace  of  a  posterior 
limb,  but  in  Halitherium  there  is  a  vestigial  femur  connected 
with  each  half  of  the  pelvis. 

Order  3.     CETACEA  1. 

In  these  mammals  the  general  form  is  more  fish-like  than  is 
the  case  even  in  the  Sirenia.  The  skin  is  generally  almost 
completely  naked,  but  hairs  are  sometimes  present  in  the  neigh- 
bourhood of  the  mouth,  especially  in  the  foetus.  In  some 
Odontoceti  vestiges  of  dermal  ossicles  have  been  described,  and 
in  Zeuglodon  the  back  was  probably  protected  by  dermal  plates. 
The  anterior  limbs  have  the  form  of  flattened  paddles,  showing 
no  trace  of  nails,  the  posterior  limb  bones  are  quite  vestigial 
or  absent,  and  there  is  never  any  external  sign  of  the  limb. 
Teeth  are  always  present  at  some  period  of  the  life  history,  but 
in  the  whalebone  whales  they  are  only  present  during  foetal 
life,  their  place  in  the  adult  animal  being  taken  by  horny 
plates  of  baleen.  In  all  living  forms  the  teeth  are  simple 
and  uniform  structures  without  enamel ;  they  have  single 
roots,  and  the  alveoli  in  which  they  are  imbedded  are  often 
incompletely  separated  from  one  another.  As  in  some  forms 
traces  of  a  replacing  dentition  have  been  described,  it  has 
been  concluded  that  the  functional  teeth  of  Cetacea  belong  to 
the  milk  dentition. 

The  texture  of  the  bones  is  spongy.  The  cervical  vertebrae 
are  very  short,  and  though  originally  seven  in  number,  are  in 
many  forms  completely  fused,  forming  one  solid  mass  (fig.  67). 
The  odontoid  process  of  the  axis  is  short  and  blunt,  or  may 

1  See  P.  J.  van  Beneden  and  P.  Gervais,  Osteographie  des  Cetaces, 
1869—80. 

K.  23 


354 


THE  VERTEBRATE  SKELETON. 


be  completely  wanting.     The  lumbar  and  caudal  vertebrae  are 
large  and  numerous,  and  as  zygapophyses  are  absent,  are  very 


FIG.  67. 


--3 


CERVICAL  VERTEBRAE  OP  A  CA'ING  WHALE  (Globicephalus 
melas)  x  £.     (Camb.  Mus.) 


1.  centrum   of  seventh   cervical 

vertebra. 

2.  neural  arch   of  seventh   cer- 

vical vertebra. 

3.  transverse  process  of  atlas. 


foramen  for  exit  of  first  spinal 

nerve. 

transverse  process  of  axis, 
fused  neural  spines  of  atlas 

and  axis. 


freely  movable  on  one  another ;  zygapophyses  are  also  absent 
from  the  posterior  thoracic  vertebrae.  The  lumbar  vertebrae 
are  sometimes  more  numerous  than  the  thoracic.  The  epi- 
physes  are  very  distinct,  and  do  not  unite  with  the  centra  till 
the  animal  is  quite  adult.  None  of  the  vertebrae  are  united 
to  form  a  sacrum,  but  the  caudal  vertebrae  have  large  chevron 
bones. 

The  skull  is  peculiarly  modified;  the  bones  forming  the 
occipital  segment  show  a  specially  strong  development,  and 
the  cranial  cavity  is  short,  high,  and  almost  spherical.  The 
supra-occipital  is  very  large  and  rises  up  to  meet  the  frontals, 


MAMMALIA.      GETACEA.  355 

thus  with  the  interparietal  completely  separating  the  parietals 
from  one  another. 

The  frontals  are  expanded,  forming  large  bony  plates, 
which  roof  over  the  orbits.  The  zygomatic  process  of  the 
squamosal  is  extremely  large  and  extends  forwards  to  meet 
the  supra-orbital  process  of  the  frontal;  the  zygomatic  process 
of  the  jugal  is  on  the  contrary  very  slender.  The  face  is 
drawn  out  into  a  long  rostrum,  formed  of  the  maxillae  and 
premaxillae  surrounding  the  vomer  and  the  mesethmoid 
cartilage.  The  maxillae  are  specially  large,  and  extend  back- 
wards so  as  to  partially  overlap  the  frontals.  The  nasals  are 
always  small,  and  the  anterior  nares  open  upwards  between 
the  cranium  and  rostrum.  The  periotics  are  loosely  connected 
with  the  other  bones  of  the  skull  and  the  tyrnpanics  are  com- 
monly large  and  dense.  The  mandible  has  hardly  any  coronoid 
process,  and  the  condyles  are  at  its  posterior  end. 

There  are  no  clavicles,  but  the  scapula  and  humerus  are 
well  developed.  The  humerus  moves  freely  in  the  glenoid 
cavity,  but  all  the  other  articulations  of  the  anterior  limb  are 
imperfect ;  the  various  bones  have  flattened  ends,  and  are 
connected  with  one  another  by  fibrous  tissue,  which  allows  of 
hardly  any  movement.  Frequently  the  carpus  is  imperfectly 
ossified. 

The  number  of  digits  in  the  manus  is  generally  five,  some- 
times four,  and  when  there  are  four  digits  it  is  the  third  and 
not  the  first  that  is  suppressed.  The  number  of  phalanges 
in  the  second  and  third  digits  almost  always  exceeds  that 
which  is  normal  in  mammals,  and  the  phalanges  are  also 
remarkable  for  having  epiphyses  at  both  ends.  The  pelvis  is 
represented  by  two  small  bones  which  lie  suspended  horizon- 
tally at  some  distance  below  the  vertebral  column  ;  in  some 
cases  vestiges  of  the  skeleton  of  the  hind  limb  are  attached  to 
thenl. 

The  Cetacea  are  divided  into  three  suborders. 

23—2 


356  THE   VERTEBRATE    SKELETON. 

Suborder  (1).     ARCHAEOCETI. 

The  members  of  this  group  are  extinct;  they  differ  from 
all  living  Cetacea  in  having  the  dentition  heterodont  and  in 
the  fact  that  the  back  was  probably  protected  by  dermal 
plates.  The  skull  is  elongated  and  depressed,  and  the  brain 
cavity  is  very  small.  The  temporal  fossae  are  large,  and 
there  is  a  strong  sagittal  crest.  The  nasals  and  premaxillae 
are  a  good  deal  larger  than  they  are  in  living  Cetacea,  and 
the  anterior  nares  are  usually  far  forward.  The  cervical  ver- 
tebrae are  not  fused  with  one  another,  and  the  lumbar 
vertebrae  are  unusually  elongated. 

The  limbs  are  very  imperfectly  known,  but  while  the 
humerus  is  much  longer  than  in  modern  Cetaceans,  it  is 
nevertheless  flattened  distally,  indicating  that  the  limb  was 
paddle-like,  and  that  there  was  scarcely  any  free  movement 
between  the  fore-arm  and  upper  arm. 

The  best  known  genus  is  Zeuglodon,  which  is  found  in 
beds  of  Eocene  age  in  various  parts  of  Europe,  and  in  Alabama. 

Suborder  (2).     MYSTACOCETI  or  BALAENOIDEA. 

These  are  the  Whalebone  Whales  or  True  Whales. 

Calcified  teeth  representing  the  milk  dentition  occur  in  the 
foetus,  but  the  teeth  are  never  functional,  and  always  dis- 
appear before  the  close  of  foetal  life.  There  is  a  definite 
though  small  olfactory  fossa.  The  palate  is  provided  with 
plates  of  baleen  or  whalebone.  The  skull  is  symmetrical,  and 
is  extremely  large  in  proportion  to  the  body.  The  nasals  are 
moderately  well  developed,  and  the  maxillae  do  not  overlap 
the  orbital  processes  of  the  f rentals.  The  lachrymals  are  small 
and  distinct  from  the  jugals.  The  tympanics  are  ankylosed 
to  the  periotics,  and  the  rami  of  the  mandible  do  not  meet  in 
a  true  symphysis.  The  ribs  articulate  only  with  the  transverse 
processes,  and  the  capitula  are  absent  or  imperfectly  deve- 
loped. Only  one  pair  of  ribs  meets  the  sternum,  which  is 
composed  of  a  single  piece. 


MAMMALIA.      CETACEA.  357 

The  group  includes  among  others  the  Right  whale  (Balaena), 
Humpbacked  whale  (Megaptera),  and  Rorqual  (Balaenoptera). 

Suborder  (3).     ODONTOCETI. 

Teeth  always  exist  after  birth  and  baleen  is  never  present. 
The  teeth  are  generally  numerous,  but  are  sometimes  few  and 
deciduous ;  the  dentition  is  homodont  (except  in  Squalodori). 
The  dorsal  surface  of  the  skull  is  somewhat  asymmetrical, 
there  is  no  trace  of  an  olfactory  fossa,  the  nasals  are  quite 
rudimentary,  and  the  hind  ends  of  the  maxillae  cover  part  of 
the  frontals ;  in  all  these  respects  the  skull  differs  from  that 
of  the  Mystacoceti.  The  lachrymal  may  either  be  united  to 
the  jugal  or  may  be  large  and  distinct.  The  tympanic  is 
not  ankylosed  to  the  periotic.  The  rami  of  the  mandible  are 
nearly  straight  and  become  united  in  a  long  symphysis.  Some 
of  the  ribs  have  well  developed  capitula  articulating  with  the 
vertebral  centra.  The  sternum  is  almost  always  composed  of 
several  pieces  as  in  other  mammals,  and  several  pairs  of  ribs 
are  connected  with  it.  There  are  always  five  digits  to  the 
manus,  though  the  first  and  fifth  are  usually  very  little 
developed. 

The  suborder  includes  the  Sperm  Whale  (Physeter),  Nar- 
whal (Monodon),  Dolphin  (Delphinus),  Porpoise  (Phocoena), 
and  many  other  living  forms  as  well  as  the  extinct  Squalodon 
which  differs  from  the  other  members  of  the  suborder  in  its 
heterodont  dentition. 

Order  4.     UNGULATA. 

This  order  includes  a  great  and  somewhat  heterogeneous 
group  of  animals,  a  large  proportion  of  which  are  extinct. 
They  all  (except  certain  extinct  forms)  agree  in  having  the 
ends  of  the  digits  either  encased  in  hoofs  or  provided  with 
broad  flat  nails.  The  teeth  are  markedly  heterodont  and 
diphyodont,  and  the  molars  have  broad  crowns  with  tubercu- 
lated  or  ridged  surfaces.  Clavicles  are  never  present  in  the 


358          THE  VERTEBRATE  SKELETON. 

adult  except  in  a  few  generalised  extinct  forms  such  as  Typo- 
ihsrium,  and  it  is  only  recently  that  vestigial  clavicles  have 
been  discovered  in  the  embryo1.  The  scaphoid  and  lunar  are 
always  distinct. 

The  order  Ungulata  may  be  subdivided  into  two  main 
groups,  Ungulata  vera  and  Subungulata. 

Section  I.     UNGULATA  VERAS. 

The  cervical  vertebrae  except  the  atlas  are  generally  opis- 
thocoelous.  The  feet  are  never  plantigrade*.  In  all  the 
living  and  the  great  majority  of  the  extinct  forms  the  digits 
do  not  exceed  four,  the  first  being  suppressed.  In  the  carpus 
the  os  magnum  articulates  freely  with  the  scaphoid,  and  is 
separated  from  the  cuneiform  by  the  lunar  and  unciform.  In 
the  tarsus  the  cuboid  articulates  with  the  astragalus  as  well  as 
with  the  calcaneum,  and  the  proximal  surface  of  the  astra- 
galus is  marked  by  a  pulley-like  groove.  All  the  bones  of 
the  carpus  and  tarsus  strongly  interlock.  These  characters 
with  regard  to  the  carpus  and  tarsus  do  not  hold  in  Macrau- 
chenia  and  its  allies.  The  humerus  never  has  an  ent-epicon- 
dylar  foramen. 

The  group  is  divided  into  two  very  distinct  suborders : — 

Suborder  (1).     ARTIODACTYLA. 

The  Artiodactyla  have  a  number  of  well  marked  charac- 
ters, one  of  the  most  obvious  being  the  fact  that  many  of  the 
most  characteristic  forms  have  large  paired  outgrowths  on  the 
frontal  bones.  These  may  be  (1)  solid  deciduous  bony  antlers, 
or  (2)  more  or  less  hollow  bony  outgrowths  which  are  sheathed 
with  permanently  growing  horn. 

1  H.  Wincza,  Morphol.  Jahrb.  xvi.,  p.  647. 

2  See  M.  Pavlow,  "Etudes  sur  1'histoire  paleontologique  des  Ongules." 
Bull.  Soc.  Moscow,  1887—1890. 

3  In  a  plantigrade  animal  the  whole  of  the  foot  is  placed  on   the 
ground  in  walking.     A  digiti  grade  animal  places  only  its  toes   on   the 
ground.     An  intermediate  condition  is  distinguished  by  the  term  sub- 
plantigrade. 


MAMMALIA.      ARTIODACTYLA.  359 

The  premolar  and  molar  teeth  are  usually  dissimilar,  the 
premolars  being  one-lobed  and  the  molars  two-lobed;  the  last 
lower  molar  of  both  the  milk  and  permanent  dentitions  is 
almost  always  three-lobed. 

The  grinding  surfaces  of  the  molar  teeth  have  a  tendency 
to  assume  one  of  two  forms.  In  the  Pigs  and  their  allies  the 
crowns  are  bunodont1,  while  in  the  more  highly  specialised 
Ruminants  the  crowns  are  selenodont1.  The  nasals  are  not 
expanded  posteriorly,  and  there  is  no  alisphenoid  canal2.  The 
thoraco-lumbar  vertebrae  are  always  nineteen.  The  symphysis 
of  the  ischia  and  pubes  is  very  elongated,  and  the  femur  has 
no  third  trochanter.  The  limbs  never  have  more  than  four 
digits,  and  are  symmetrical  about  a  line  drawn  between  the 
third  and  fourth  digits ;  the  digits,  on  the  other  hand,  are 
never  symmetrical  in  themselves.  The  astragalus  has  pulley- 
like  surfaces  both  proximally  and  distally,  and  articulates  with 
the  navicular  and  cuboid  by  two  nearly  equal  facets.  The 
calcaneum  articulates  with  the  lower  end  of  the  fibula  when 
that  bone  is  fully  developed. 

In  the  Artiodactyla  are  included  the  following  living 
groups : — 

a.  Suina.     Pigs  and  Hippopotami. 

b.  Tylopoda.     Camels  and  Llamas. 

c.  Tragulina.     Chevrotains. 

d.  Ruminantia  or   Pecora.     Deer,    giraffes,   oxen,    sheep 
and  antelopes. 

Suborder  (2).     PfiRissoDACTYLA3. 

In  this  group  there  are  never  any  bony  outgrowths  from 
the  frontals.  The  grinding  teeth  form  a  continuous  series, 
the  posterior  premolars  resembling  the  molars  in  complexity, 
and  the  last  lower  molar  generally  has  no  third  lobe.  The 

1  See  p.  345.  2  See  p.  401. 

3  See  E.  D.  Cope,  "The  Perissodactyla,"  Amer.  Natural,  1887. 


360  THE   VERTEBRATE    SKELETON. 

cervical  vertebrae  with  the  exception  of  the  atlas  almost 
always  have  markedly  opisthocoelous  centra,  but  in  Macrau- 
chenia  they  are  flat.  The  nasals  are  expanded  posteriorly,  and 
an  alisphenoid  canal  is  present.  The  thoraco-lumbar  vertebrae 
are  never  less  than  twenty-two  in  number  and  are  usually 
twenty-three.  The  femur  has  a  third  trochanter  (except  in 
Chalicotherium).  The  third  digit  of  the  manus  and  pes  is 
symmetrical  in  itself,  and  larger  than  the  others,  and  in  some 
cases  the  other  digits  are  quite  vestigial.  The  number  of  the 
digits  of  the  pes  is  always  odd.  The  astragalus  is  abruptly 
truncated  distally,  and  the  facet  by  which  it  articulates  with 
the  cuboid,  is  much  smaller  than  that  by  which  it  articulates 
with  the  navicular.  The  calcaneum  does  not  articulate  with 
the  fibula,  except  in  Macrauchenia,  The  group  includes  many 
extinct  forms,  and  the  living  families  of  the  Tapirs,  Horses 
and  Asses,  and  Rhinoceroses. 


Section  II.     SUBUNGULATA. 

In  this  group  is  placed  a  heterogeneous  collection  of 
animals,  the  great  majority  of  which  are  extinct.  There  is 
really  no  characteristic  which  is  common  to  them  all,  and 
which  serves  to  distinguish  them  as  a  group  from  the  Ungulata 
vera.  But  the  most  distinctive  character  common  to  the 
greatest  number  of  them  is  to  be  found  in  the  carpus,  whose 
bones  in  most  cases  retain  their  primitive  relation  to  one 
another,  the  os  magnum  articulating  with  the  lunar  and  some- 
times just  meeting  the  cuneiform,  but  in  living  forms  at  any 
rate  not  articulating  with  the  scaphoid.  The  feet  frequently 
have  five  functional  digits,  and  may  be  plantigrade.  The 
proximal  surface  of  the  astragalus  is  generally  flattened  in- 
stead of  being  pulley -like  as  in  Ungulata  vera. 


MAMMALIA.      SUBUNGULATA.  361 

Suborder  (1).     TOXODONTIA. 

This  suborder  includes  some  very  aberrant  extinct  South 
American  ungulates,  which  have  characters  recalling  the 
Proboscidea,  both  groups  of  Ungulata  vera,  and  the  Rodentia. 
The  limbs  are  subplantigrade  or  digitigrade,  and  the  digits 
are  three,  rarely  five,  in  number,  the  third  being  most 
developed.  The  carpus  resembles  that  of  the  Ungulata  vera, 
in  that  the  bones  interlock  and  the  magnum  articulates  with 
the  scaphoid.  In  the  tarsus,  however,  the  bones  do  not 
interlock.  The  astragalus  has  a  pulley-like  proximal  sur- 
face (except  in  Astrapotherium,  in  which  it  is  flat),  and 
articulates  only  with  the  navicular,  not  meeting  the  cuboid. 
The  calcaneum  has  a  large  facet  for  articulation  with  the 
fibula,  as  in  Artiodactyla.  There  is  no  alisphenoid  canal,  and 
the  orbit  is  confluent  with  the  temporal  fossa.  Some  of  the 
forms  (e.g.  Nesodon)  referred  to  this  group  have  the  typical 
mammalian  series  of  forty-four  teeth,  but  in  others  the  canines 
are  undeveloped.  In  Toxodon  all  the  cheek-teeth  have  persist- 
ent pulps,  while  in  Nesodon  and  Astrapotherium  they  are  rooted. 
A  clavicle  is  sometimes  present  (Typotherium),  and  the  femur 
sometimes  has  a  third  trochanter  (Typotherium  and  Astra- 
potherium), sometimes  is  without  one  (Toxodon). 

The  remains  of  these  curious  Ungulates  have  been  found 
in  beds  of  late  Tertiary  age  in  South  America. 

Suborder    (2).       CONDYLARTHRA1. 

This  group  includes  some  comparatively  small  extinct 
ungulates,  which  are  best  known  from  the  Lower  Eocene  of 
Wyoming,  though  their  remains  have  also  been  found  in 
deposits  of  similar  age  in  France  and  Switzerland.  Their 

1  See  E.  D.  Cope,  "The  Condylarthra,"  Amer.  Natural.,  1884,  and 
"Synopsis  of  the  Vertebrates  of  the  Puerco  series,"  Tr.  Amer.  Phil.  Soc., 
1888.  0.  C.  Marsh,  "A  new  order  of  extinct  Eocene  Mammals  (Meso- 
dactyla),"  Amer.  J.  Sci.,  1892. 


362          THE  VERTEBRATE  SKELETON. 

characters  are  little  specialised,  and  they  show  relationship  on 
the  one  hand  to  the  Ungulata  vera  and  on  the  other  to  the 
Hyracoidea.  They  also  have  characters  allying  them  to  the 
Carnivora.  They  generally  have  the  typical  mammalian 
series  of  forty-four  teeth,  the  molars  being  brachydont  and 
generally  bunodont.  The  premolars  are  more  simple  than  the 
molars.  The  limbs  are  plantigrade,  and  have  five  digits  with 
rather  pointed  ungual  phalanges.  The  os  magnum,  as  in  living 
Subungulates,  articulates  with  the  lunar,  not  reaching  the 
scaphoid.  The  astragalus  has  an  elongated  neck,  a  pulley-like 
proximal  and  a  convex  distal  articular  surface,  and  does  not 
articulate  with  the  cuboid.  The  humerus  has  an  ent-epicondylar 
foramen,  and  the  femur  has  a  third  trochanter.  The  best 
known  genus  is  Phenacodus ;  it  is  perhaps  the  most  primitive 
ungulate  whose  skeleton  is  thoroughly  well  known,  and  is  of 
special  interest  from  the  fact  that  it  is  regarded  as  the  lowest 
stage  in  the  evolutionary  series  of  the  horse.  Its  remains 
are  found  in  the  Lower  Eocene  of  Wyoming. 

Suborder  (3).     HYRACOIDEA  1. 

This  group  of  animals  is  very  isolated,  having  no  very  close 
allies,  either  living  or  extinct.  The  digits  are  provided  with 
flat  nails,  except  the  second  digit  of  the  pes,  which  is  clawed. 
Canine  teeth  are  absent,  and  the  dental  formula  is  usually 

given  as  i  -,  c    ^,  pm  -,  ra  ^.     The  upper  incisors  are  long 

and  curved,  and  have  persistent  pulps  as  in  Rodents ;  their 
terminations  are,  however,  pointed,  not  chisel-shaped,  as  in 
Rodents.  The  lower  incisors  have  pectinated  edges.  The 
grinding  teeth  have  a  pattern  much  like  that  in  Rhinoceros. 
In  the  skull  (fig.  83)  the  postorbital  processes  of  the  frontal 
and  jugal  almost  or  quite  meet.  The  jugal  forms  part  of  the 

1  See  0.  Thomas,  "On  the  species  of  Hyracoidea,"  P.  Z.  S.,  1892, 
p.  50. 


MAMMALIA.      SUBUNGULATA.  363 

glenoid  cavity  for  articulation  with  the  mandible,  and  also 
extends  forwards  so  as  to  meet  the  lachrymal.  There  is  an 
alisphenoid  canal.  There  are  as  many  as  twenty-one  or  twenty- 
two  thoracic  vertebrae,  and  the  number  of  thoraco- lumbar 
vertebrae  reaches  twenty-eight  or  thirty.  There  are  no  clavi- 
cles, and  the  scapula  has  no  acromion ;  the  coracoid  process 
is,  however,  well  developed.  The  ulna  is  complete.  In  the 
manus  the  second,  third  and  fourth  digits  are  approximately 
equal  in  size,  the  fifth  is  smaller,  and  the  first  is  vestigial. 
The  femur  has  a  slight  ridge  representing  the  third  trochanter. 
The  fibula  is  complete,  but  is  generally  fused  with  the  tibia 
proximally.  There  is  a  complicated  articulation  between  the 
tibia  and  astragalus,  which  has  a  pulley-like  proximal  surface. 
In  the  pes  the  three  middle  digits  are  well  developed,  but  there 
is  no  trace  of  a  hallux,  and  the  fifth  digit  is  represented  only 
by  a  vestigial  metatarsal. 

The  only  representatives  of  the  suborder  are  some  small 
animals  belonging  to  the  genus  Procavia  (Hyrax),  which  is 
found  in  Africa  and  Syria ;  some  of  the  species  are  by  many 
authors  placed  in  a  distinct  genus  Dendrohyrax. 

Suborder  (4).     AMBLYPODA1. 

This  suborder  includes  a  number  of  primitive  extinct 
Ungulates,  many  of  which  are  of  great  size.  Their  most 
distinguishing  characteristics  are  afforded  by  the  extremities. 
In  the  carpus  the  bones  interlock  a  little  more  than  is  the  case 
in  most  Subungulata,  and  the  corner  of  the  os  magnum  reaches 
the  scaphoid,  while  the  lunar  articulates  partially  with  both 
magnum  and  unciform,  instead  of  only  with  the  magnum. 
In  the  tarsus  the  cuboid  articulates  with  both  the  calcaneum 
and  the  astragalus,  which  is  remarkably  flat.  The  manus  and 
pes  are  short,  nearly  or  quite  plantigrade,  and  have  the  full 
number  of  digits.  The  cranial  cavity  is  singularly  small. 

1  See  E.  D.  Cope,  "The  Amblypoda,"  Amer.  Natural,  1884  and  1885. 


364  THE  VERTEBRATE  SKELETON. 

Canine  teeth  are  present  in  both  jaws,  and  the  grinding  teeth 
have  short  crowns,  marked  by  V-shaped  ridges.  The  pelvis  is 
large,  the  ilia  are  placed  vertically,  and  the  ischia  do  not  take 
part  in  the  ventral  symphysis. 

The  best  known  animals  belonging  to  this  suborder  are  the 
Uintatheriidae  (Dinocerata)1,  found  in  the  Upper  Eocene  of 
Wyoming.  They  are  as  large  as  elephants,  and  are  charac- 
terised by  the  long  narrow  skull  drawn  out  into  three  pairs 
of  rounded  protuberances,  by  the  strong  occipital  crest,  and 
by  the  very  large  upper  canines. 

Suborder  (5).     PROBOSCIDEA. 

This  suborder  includes  the  largest  of  land  mammals,  the 
Elephants,  and  certain  of  their  extinct  allies.  The  limbs  are 
strong,  and  are  vertically  placed ;  the  proximal  segment  is  the 
longest,  and  the  manus  and  pes  are  pentedactylate  and  sub- 
plantigrade.  The  digits  are  all  enclosed  in  a  common  integu- 
ment, and  each  is  provided  with  a  broad  hoof.  The  vertebral 
centra  are  much  flattened  and  compressed,  especially  in  the  cer- 
vical region.  The  number  of  thoracic  vertebrae  is  very  great, 
reaching  twenty.  The  skull  (figs.  96  and  97)  is  extremely  large, 
this  being  due  to  the  great  development  of  air  cells,  which 
takes  place  in  nearly  all  the  bones  of  the  adult  skull.  In  the 
young  skull  there  are  hardly  any  air  cells,  and  the  growth  of 
the  cranial  cavity  does  not  by  any  means  keep  pace  with  the 
growth  of  the  skull  in  general.  The  supra-occipital  is  very 
large,  and  forms  a  considerable  part  of  the  roof  of  the  skull. 
The  nasals  and  jugals  are  short,  and  the  premaxillae  very 
large.  The  rami  of  the  mandible  meet  in  a  long  symphysis,  and 
the  ascending  portion  is  very  high.  Canine  teeth  are  absent, 
and  the  incisors  have  the  form  of  ever-growing  tusks  composed 
mainly  of  dentine;  in  living  forms  they  are  present  in  the 
upper  jaw  only.  The  grinding  teeth  are  large,  and  in  living 

1  See  0.  C.  Marsh,  "The  Dinocerata,"  U.  S.  Geol.  Survey,  1884, 
vol.  x. 


MAMMALIA.      RODENTIA.  365 

forms  have  a  very  complex  structure  and  mode  of  succession. 
In  some  of  the  extinct  forms,  such  as  Mastodon  and  especially 
Dinotkerium,  the  teeth  are  much  more  simple.  In  every  case 
the  teeth  have  the  same  general  structure,  consisting  of  a 
series  of  ridges  of  dentine,  coated  with  enamel.  In  the  more 
specialised  forms  the  valleys  between  the  ridges  are  filled  up 
with  cement.  The  acromion  of  the  scapula  has  a  recurved 
process,  similar  to  that  often  found  in  rodents.  Clavicles  are 
absent.  The  radius  and  ulna  are  not  ankylosed,  but  are 
incapable  of  any  rotatory  movement.  All  the  bones  of  the 
extremities  are  very  short  and  thick ;  the  scaphoid  articulates 
regularly  with  the  trapezoid  and  the  lunar  with  the  magnum. 
The  ilia  are  vertically  placed,  and  are  very  much  expanded  ; 
the  ischia  and  pubes  are  small,  and  form  a  short  symphysis. 
The  femur  has  no  third  trochanter,  and  the  tibia  and  fibula 
are  distinct.  The  fibula  articulates  with  the  calcaneum,  and 
the  astragalus  is  very  flat. 

Here  brief  reference  may  be  made  to  the  TiLLODONTiA1,  a 
group  of  extinct  mammals  found  in  the  Eocene  beds  of  both 
Europe  and  North  America.  They  seem  to  connect  together 
the  Ungulata,  Rodentia,  and  Carnivora. 

The  skull  resembles  that  of  bears,  but  the  grinding  teeth 
are  of  Ungulate  type,  while  the  second  incisors  resemble  those 
of  rodents,  and  have  persistent  pulps.  The  femur  has  a  third 
trochanter,  and  the  feet  resemble  those  of  bears  in  being 
plantigrade  and  having  pointed  ungual  phalanges,  differing, 
however,  in  having  the  scaphoid  and  lunar  distinct. 

Order  5.     RODENTIA. 

The  Rodents  form  a  very  large  and  well-defined  group  of 

mammals  easily  distinguishable  by  their  peculiar  dentition. 

Canines  are  absent,  and  the  incisors  are  very  large  and  curved, 

growing  from  persistent  pulps.    They  are  rectangular  in  section 

1  See  0.  C.  Marsh,  Amer.  J.  Set.,  1875  and  1876. 


366          THE  VERTEBRATE  SKELETON. 

and  are  much  more  thickly  coated  with  enamel  on  their 
anterior  face  than  elsewhere  ;  consequently,  as  they  wear  down 
they  acquire  and  retain  a  chisel-shaped  (scalpriform)  edge. 
There  is  never  more  than  one  pair  of  incisors  in  the  mandible, 
and  except  in  the  Hares  and  Rabbits,  there  is  similarly  only  a 
single  pair  in  the  upper  jaw.  These  animals  are,  too,  the  only 
rodents  which  have  well  developed  deciduous  incisors.  There 
is  always  a  long  diastema  separating  the  incisors  from  the 
grinding  teeth.  The  grinding  teeth,  which  are  arranged  in  a 
continuous  series,  vary  in  number  from  two  to  six  in  the  upper 
jaw,  and  from  two  to  five  in  the  lower  jaw.  The  number  of 
premolars  is  always  below  the  normal,  often  they  are  altogether 
wanting,  but  generally  they  are  ^.  Sometimes  the  grinding 
teeth  form  roots,  sometimes  they  grow  persistently. 

The  premaxillae  are  always  large,  and  the  orbits  always  com- 
municate freely  with  the  temporal  fossae.  The  condyle  of  the 
mandible  is  elongated  from  before  backwards,  and  owing  to 
the  absence  of  a  postglenoid  process  to  the  squamosal,  a  back- 
ward and  forward  motion  of  the  jaw  can  take  place.  The 
zygomatic  arch  is  complete,  but  the  jugal  is  short  and  only 
forms  the  middle  of  it.  The  palate  is  small,  being  some- 
times, as  in  the  hares,  narrowed  from  before  backwards, 
sometimes  as  in  the  mole-rats  (Bathyerginae)  narrowed  trans- 
versely. 

The  thoraco-lumbar  vertebrae  are  usually  nineteen  in 
number.  Clavicles  are  generally  present,  and  the  acromion 
of  the  scapula  is  commonly  very  long.  The  feet  are  as  a  rule 
plantigrade,  and  provided  with  five  clawed  digits. 

There  are  two  main  groups  of  Rodentia  ;  the  Duplici- 
dentata,  or  Hares  and  Rabbits,  which  have  two  pairs  of  upper 
incisors,  whose  enamel  extends  round  to  the  posterior  surface ; 
and  the  Simplicidentata,  in  which  there  is  only  a  single  pair 
of  upper  incisors,  whose  enamel  is  confined  to  the  anterior 
surface.  This  group  includes  all  the  Rodents  except  the 
Hares  and  Rabbits. 


MAMMALIA.      CARNIVORA.  367 


Order  6.     CARNIVORA. 

The  living  Carnivora  form  a  natural  and  well-marked 
group,  but  as  is  the  case  with  so  many  other  groups  of 
animals,  when  their  extinct  allies  are  included,  it  becomes 
impossible  to  readily  define  them. 

The  raanus  and  pes  never  have  less  than  four  well-developed 
digits,  and  these  are  nearly  always  provided  with  more  or  less 
pointed  nails,  generally  with  definite  claws.  The  hallux  and 
pollex  are  never  opposable.  The  dentition  is  diphyodont  and 
markedly  heterodont.  The  teeth  are  always  rooted,  except 
in  the  case  of  the  canines  of  the  Walrus.  The  incisors  are 
generally  f,  and  are  comparatively  small,  while  the  canines 
are  large,  pointed,  and  slightly  recurved.  The  cheek  teeth  are 
variable,  and  are  generally  more  or  less  compressed  and 
pointed ;  sometimes  their  crowns  are  flattened  and  tuber- 
culated,  but  they  are  never  divided  into  lobes  by  deep  infoldings 
of  enamel.  The  squamosal  is  drawn  out  into  a  postglenoid 
process,  and  the  mandible  has  a  large  coronoid  process.  The 
condyle  of  the  mandible  is  transversely  elongated,  and  the 
glenoid  fossa  is  very  deep;  in  consequence  of  this  arrangement 
the  mandible  can  perform  an  up  and  down  movement  only, 
any  rotatory  or  back  and  fore  movement  being  impossible. 
The  jugal  is  large,  and  the  zygomatic  arch  generally  strong, 
while  the  orbit  and  temporal  fossa  are  in  most  cases  completely 
confluent.  The  scapula  has  a  large  spine.  The  clavicle  is 
never  complete  and  is  often  absent,  this  forming  an  important 
distinction  between  the  skeleton  of  a  Carnivore  and  of  any 
Insectivore  except  Potamogale.  The  humerus  often  has  an 
ent-epicondylar  foramen,  and  the  radius  and  ulna,  tibia  and 
fibula  are  always  separate.  The  manus  is  often  capable  of  the 
movements  of  pronation  and  supination,  and  the  scaphoid, 
lunar  and  centrale  are  in  living  forms  always  united  together. 

The  order  Carnivora  includes  three  suborders. 


368  THE   VERTEBRATE    SKELETON. 

Suborder  (1).     CREODONTA1. 

This  suborder  contains  a  number  of  extinct  Carnivora, 
which  present  very  generalised  characters. 

The  cranial  cavity  is  very  small ;  and  the  fourth  upper  pre- 
molar  and  first  lower  molar  are  not  differentiated  as  carnassial 
teeth2,  as  they  are  in  modern  Carnivora.  The  Creodonta  also 
differ  from  modern  Carnivora  in  the  fact  that  the  scaphoid  and 
lunar  are  usually  separate,  and  that  the  femur  has  a  third 
trochanter.  The  feet  are  plantigrade. 

They  resemble  the  Condylarthra,  another  very  generalised 
group,  in  having  an  ent-epicondylar  foramen. 

They  occurred  throughout  the  Tertiary  period  in  both 
Europe  and  North  America,  and  have  also  been  found  in  India. 
One  of  the  best  known  genera  is  Hyaenodon. 

Suborder  (2).     CARNIVORA  VERA  or  FISSIPEDIA. 

The  skeleton  is  mainly  adapted  for  a  terrestrial  mode  of 
life,  and  the  hind  limbs  have  the  normal  mammalian  position. 
In  almost  every  case  the  number  of  incisors  is  §.  Each  jaw 
always  has  one  specially  modified  carnassial  or  sectorial  tooth 
which  bites  like  a  scissors  blade  against  a  corresponding  tooth 
in  the  other  jaw.  In  front  of  it  the  teeth  are  always  more 
or  less  pointed,  while  behind  it  they  are  more  or  less  broadened 
and  tuberculated.  In  the  manus  the  first  digit,  and  in  the 
pes  the  first  and  fifth  digits  are  never  longer  than  the  rest, 
and  the  digits  of  both  limbs  are  almost  invariably  clawed. 
Some  forms  are  plantigrade,  some  digitigrade,  some  sub- 
plantigrade.  The  group  includes  all  the  ordinary  terrestrial 
Carnivora,  and  is  divided  into  three  sections  : 

1  E.  D.  Cope,  "The  Creodonta,"  Amer.  Natural.,  1884.     W.  B.  Scott, 
"Revision  of  the  N.  American  Creodonta,"  P.  Ac.  Philad.,  1892. 

2  See  next  paragraph. 


MAMMALIA.      PINNIPEDIA.  369 

JEluroidea1,  including  the  cats,  civets,  hyaenas,  and  allied 
forms. 

Cynoidea,  including  the  dog  tribe. 

Arctoidea,  including  the  bears,  raccoons,  weasels,  and  allied 
forms. 

Suborder  (3).      PiNNiPEDiA2. 

In  this  suborder  the  limbs  are  greatly  modified  and  adapted 
for  a  more  or  less  purely  aquatic  life,  the  proximal  and  middle 
segments  of  the  limbs  are  shortened,  while  the  distal  segment, 
especially  in  the  leg,  is  much  elongated  and  expanded.  There  are 
always  five  well-developed  digits  to  each  limb,  and  in  the  pes  the 
first  and  fifth  digits  are  generally  larger  than  the  others.  The 
digits  generally  bear  straight  nails  instead  of  claws,  but  even 
nails  are  sometimes  absent.  There  is  no  carnassial  tooth,  and 
the  teeth  in  other  ways  differ  considerably  from  those  of  Carni- 
vora  vera.  The  incisors  are  always  fewer  than  § ;  while  the 
cheek  teeth  generally  consist  of  four  premolars  and  one  molar, 
all  of  very  uniform  character,  being  compressed  with  conical 
crowns,  and  never  more  than  two  roots. 

The  suborder  includes  three  families — Otariidae  (Eared 
Seals),  Trichechidae  (Walrus),  and  Phocidae  (Seals). 

Order  7.     INSECTIVORA3. 

This  order  contains  a  large  number  of  small  generally  ter- 
restrial mammals.  The  limbs  are  plantigrade  or  subplantigrade, 
and  are  generally  pentedactylate.  All  the  digits  are  armed 
with  claws,  and  the  pollex  and  hallux  are  not  opposable.  The 
teeth  are  diphyodont,  heterodont,  and  rooted.  The  cheek  teeth 

1  St  G.  Mivart,  The  Cat,  London,  1881. 

2  St  G.  Mivart,  P.  Z.  S.,  1885. 

3  St  G.  Mivart,  "On  the  Osteology  of  Insectivora, "  J.  Anat.  PhysioL 
norm,  path.,  1867  and  1868,  and  P.  Z.  S.,  1871.    G.  E.  Dobson,  Monograph 
of  the  Insectivora,  London,  1882—90. 

H.  24 


370          THE  VERTEBRATE  SKELETON. 

have  tuberculated  crowns,  and  there  are  never  less  than  two 
pairs  of  incisors  in  the  mandible  ;  often  the  incisors,  canines, 
and  premolars  are  not  clearly  differentiated  from  one  another, 
and  special  carnassial  teeth  are  never  found.  The  cranial  cavity 
is  small,  and  the  facial  part  of  the  skull  is  generally  much 
developed ;  often  the  zygomatic  arch  is  incomplete.  Clavicles 
are  well  developed  (except  in  Potamogale),  and  the  hum  ems 
generally  has  an  ent-epicondylar  foramen.  The  femur  fre- 
quently has  a  ridge  representing  the  third  trochanter.  There 
are  two  suborders  : 

Suborder  (1).     DERMOPTERA. 

This  suborder  includes  only  a  very  aberrant  arboreal  genus 
Galeopitkecus,  remarkable  for  its  greatly  elongated  limb  bones, 
and  peculiar  dentition.  The  incisors  of  the  lower  jaw  are 
deeply  pectinated  or  divided  by  several  vertical  fissures,  the 
canines  and  outer  upper  incisors  have  two  roots.  Ossified 
intercentra  occur  in  the  thoraco-lumbar  region  of  the  vertebral 
column. 

Suborder  (2).     INSECTIVORA  VERA. 

This  suborder  includes  all  the  ordinary  Insectivora,  such  as 
moles,  shrews  and  hedgehogs.  The  upper  and  lower  incisors 
are  conical,  not  pectinated. 

Order  8.     CniROPTERA1. 

This  order  is  perhaps  the  best  marked  and  most  easily 
defined  of  all  the  orders  of  mammals.  The  anterior  limbs 
form  true  wings  and  the  whole  skeleton  is  modified  in  relation 
to  flight. 

The  anterior  limbs  are  vastly  larger  than  the  posterior ; 
for  all  the  bones  except  the  carpals  are  much  elongated,  and 

1  See  G.  E.  Dobson,  Brit.  Mm.  Catalogue  of  Chiroptera,  1878.  See 
also  other  papers  by  the  same  author  and  by  Oldfield  Thomas. 


MAMMALIA.      CHIKOPTERA.  371 

this  applies  specially  to  the  phalanges  of  all  the  digits  except 
the  pollex. 

The  pollex  is  clawed  and  so  is  sometimes  the  second  digit ; 
the  other  digits  of  the  manus  are  without  nails  or  claws.  The 
teeth  are  divisible  into  the  four  usual  types  and  the  series 

91  33 

never  exceeds  i  ^    c   -=-  pm    -  w  -  x  2,  total  38.      The  milk 

O  1  DO 

teeth  are  quite  unlike  the  permanent  teeth.  The  orbit  is  not 
divided  by  bone  from  the  temporal  fossa.  The  vertebral 
column  is  short,  and  in  old  animals  the  trunk  vertebrae 
have  a  tendency  to  become  partially  fused  together.  The 
cervical  vertebrae  are  remarkably  wide,  and  the  development 
of  spinous  processes  is  everywhere  slight.  The  presternum 
has  a  prominent  keel  for  the  attachment  of  the  pectoral  muscles. 
The  clavicles  are  very  long  and  strong,  and  the  scapula  has  a 
long  spine  and  coracoid  process.  The  ulna  is  vestigial,  con- 
sisting only  of  a  proximal  end  ankylosed  to  the  radius.  All 
the  carpals  of  the  proximal  row — the  scaphoid,  lunar  and 
cuneiform — are  united,  forming  a  single  bone.  The  pelvis  is 
very  weak  and  narrow,  and  only  in  the  Rhinolophidae  do  the 
pubes  meet  in  a  symphysis.  The  anterior  caudal  vertebrae  are 
frequently  united  to  the  ischia.  The  fibula  is  generally  ves- 
tigial, and  the  knee  joint  is  directed  backwards  instead  of 
forwards.  The  pes  has  five  slender  clawed  digits,  and  the 
calcaneum  is  often  drawn  out  into  a  spur  which  helps 
to  support  the  membrane  connecting  the  hind  limbs  with  the 
tail. 

There  are  two  suborders  of  Chiroptera  : 

1.  The  MEGACHIROPTERA  or  Flying  foxes,  which  almost 
always  have  smooth  crowns  to  the  molar  teeth,  and  the  second 
digit  of  the  manus  clawed. 

2.  The  MICROCHIROPTERA  including  all  the  ordinary  bats 
which  have  cusped  molar  teeth,  and  the  second  digit  of  the 
manus  clawless. 

24—2 


372  THE   VERTEBRATE   SKELETON. 

Order  9.     PRIMATES. 

The  dentition  is  diphyodont  and  heterodont,  the  incisors 
generally  number  f ,  and  the  molars,  except  in  the  Hapalidae 
(Marmosets),  are  f .  The  cheek  teeth  are  adapted  for  grind- 
ing, and  the  molars  are  more  complex  than  the  premolars. 
A  process  from  the  jugal  meets  the  postorbital  process  of  the 
frontal  completing  the  postorbital  bar. 

The  clavicle  is  well  developed,  and  the  radius  and  ulna 
are  never  united.  The  scaphoid  and  lunar  of  the  carpus, 
and  commonly  also  the  centrale,  remain  distinct  from  one 
another.  As  a  rule  both  manus  and  pes  have  five,  digits, 
but  the  pollex  may  be  vestigial.  The  pollex  is  opposable  to 
the  other  digits,  and  so  is  the  hallux  except  in  Man;  the 
digits  are  almost  always  provided  with  flat  nails.  The  hu- 
merus  has  no  ent-epicondylar  foramen  and  the  femur  has  no 
third  trochanter. 

The  order  Primates  is  divisible  into  two  suborders  : 

Suborder  (1).     LEMUROIDEA. 

The  skull  has  the  orbit  communicating  freely  with  the 
temporal  fossa  beneath  the  postorbital  bar  (except  in  Tar- 
sius}. The  lachrymal  foramen  is  external  to  the  margin  of 
the  orbit.  Both  pollex  and  hallux  are  well  developed.  In 
the  pes  the  second  digit  is  terminated  by  a  long  pointed  claw, 
and  so  is  also  the  third  in  Tarsius.  The  lumbar  region  of 
the  vertebral  column  is  long,  sometimes  including  as  many  as 
nine  vertebrae.  Besides  the  Lemurs  the  group  includes  the 
aberrant  Tarsius  and  Chiromys. 

Suborder  (2).     ANTHROPOIDEA. 

The  skull  has  the  orbit  almost  completely  shut  off  from 
the  temporal  fossa,  and  the  lachrymal  foramen  is  situated 
within  the  orbit.  The  pollex  is  sometimes  vestigial  or  absent. 


MAMMALIA.      PRIMATES.  373 

The  second  digit  of  the  pes  has  a  flattened  nail  except  in  the 
Hapalidae,  in  which  all  the  digits  of  the  pes  except  the  hallux 
are  clawed. 

The  Anthropoidea  are  divided  into  five  families  : 

1.  Hapalidae  or  Marmosets. 

2.  Cebidae  or  American  Monkeys. 

3.  Cercopithecidae  or  Old  World  Monkeys. 

4.  Simiidae  or  Anthropoid  Apes. 

5.  Hominidae  or  Men. 


CHAPTER   XXI. 
THE    SKELETON    OF    THE    DOG1    (Canis  familiaris). 

I.     EXOSKELETON. 

The  exoskeleton  of  the  dog  includes  three  sets  of  structures : 
1.  hairs,  2.  claws,  3.  teeth.  Hairs  and  claws  are  epidermal 
exoskeletal  structures,  while  teeth  are  partly  of  dermal,  and 
partly  of  epidermal  origin. 

1.  Hairs  are  delicate  epidermal  structures  which  grow 
imbedded  in  little  pits  or  follicles  in   the  dermis.     Specially 
large  hairs  forming  the  vibrissae  or  whiskers  grow  attached 
to  the  upper  lip. 

2.  Claws  are  horny  epidermal  sheaths,  one  of  which  fits 
on  to  the  pointed  distal  phalanx  of  each  digit.     They  are 
sharply  curved  structures,  and  being  in  the  dog  non-retractile, 
their  points  are  commonly  much  blunted  by  friction  with  the 
ground.     The  claws  of  the  pollex,  and  of  the  hallux  when  it  is 
present,  however  do  not  meet  the  ground,  and  therefore  remain 
comparatively  sharp. 

3.  Teeth2.     Although  as  regards  their  mode  of  origin, 
teeth  are  purely  exoskeletal  or  tegumentary  structures,  they 

1  W.  Ellenberger  and  H.  Baum,  Anatomic  des  Hundes,  Berlin,  1891. 

2  T.  H.  Huxley,  "Dental  and  cranial  characters  of  the  Canidae," 
P.  Z.  S.  1880. 


THE  SKELETON  OF  THE  DOG.   THE  TEETH. 


375 


become  so  intimately  connected  with  the  skull  that  they  appear 
to  belong  to  the  endoskeleton. 

Each  tooth,  as  has  been  already  described,  consists  of  three 
distinct  tissues,  dentine  and  cement  of  dermal  origin,  and 
enamel  of  epidermal  origin. 


FIG.  68.     DENTITION  OF  A  DOG  (Canis  familiaris)  x  ^.     (Camb.  Mus.) 
i  2.     second  incisor.  pm  1,  pm  4.     first  and  fourth  pre- 


c.     canine. 


molars. 
m  1.     first  molar. 


The  teeth  of  the  dog  (fig.  68)  form  a  regular  series  arranged 
along  the  margins  of  both  upper  and  lower  jaws,  and  imbedded 
in  pits  or  alveoli  of  the  maxillae,  premaxillae,  and  mandibles. 


376  THE  VERTEBRATE  SKELETON. 

They  are  all  fixed  in  the  bone  by  tapering  roots,  and  none  of 
them  grow  from  persistent  pulps. 

They  are  divisible  into  four  distinct  groups,  the  incisors, 
canines,  premolars  and  molars.  There  are  three  incisors, 
one  canine  and  four  premolars  on  each  side  of  each  jaw. 
But  while  there  are  three  molars  on  each  side  of  the  lower 
jaw,  the  last  is  wanting  in  the  upper  jaw.  The  dentition  of 
the  dog  may  then  be  represented  by  the  formula 

31  42 

i^    c  j   pm  ^    m  -  x  2  =  42. 

In  each  jaw  there  is  one  large  specially  modified  tooth 
called  the  carnassial,  the  teeth  in  front  of  this  are  more  or 
less  pointed  and  compressed,  while  those  behind  it  are  more  or 
less  flattened  and  tuberculated. 

Teeth  of  the  upper  jaw. 

The  first  and  second  incisors  are  small  teeth  with  long 
conical  roots  and  somewhat  chisel-shaped  crowns.  Surround- 
ing the  base  of  the  crown  there  is  a  rather  prominent  ridge, 
terminated  laterally  by  a  pair  of  small  cusps.  This  ridge,  the 
cinglllum,  serves  to  protect  the  edge  of  the  gums  from  injury 
by  the  hard  parts  of  food.  The  third  incisor  is  a  good  deal 
like  the  others  but  larger,  and  has  the  cingulum  well  developed 
though  not  terminated  by  lateral  cusps.  All  the  incisors 
are  borne  by  the  premaxillae,  the  remaining  teeth  by  the 
maxillae. 

The  canine  is  a  large  pointed  tooth,  slightly  recurved  and 
with  a  long  tapering  root. 

The  premolars  are  four  in  number,  and  in  all  the  cingu- 
lum is  fairly  well  seen.  The  first  is  a  very  small  tooth  with  a 
single  tapering  root,  the  second  and  third  are  larger  and  have 
two  roots,  while  the  fourth,  the  carnassial,  is  much  the  largest 
and  has  three  roots.  Each  of  the  second,  third  and  fourth  pre- 
molars has  a  stout  blade,  the  middle  portion  of  which  is  drawn 
out  into  a  prominent  cone  ;  the  posterior  part  of  the  fourth 


THE    SKELETON    OF   THE   DOG.      THE   TEETH.          377 

premolar  forms  a  compressed  ridge,  and  at  the  antero-internal 
edge  of  the  tooth  there  is  a  small  inner  tubercle. 

The  two  molar  teeth  are  of  very  unequal  size.  The  first, 
which  has  two  anterior  roots  and  one  posterior,  is  wider  than 
it  is  long,  its  outer  portion  being  produced  into  two  prominent 
cusps,  while  its  inner  portion  is  depressed.  The  second  molar 
is  a  small  tooth  resembling  the  first  in  its  general  appearance, 
but  with  much  smaller  outer  cusps. 

Teeth  of  the  lower  jaw. 

The  three  incisors  of  the  lower  jaw  have  much  the  same 
character  as  the  first  two  of  the  upper  jaw  ;  while  the  canine 
is  identical  in  character  with  that  of  the  upper  jaw. 

The  four  premolars  gradually  increase  in  size  from  the 
first  to  the  last,  but  none  are  very  large.  The  first  premolar 
is  a  single-rooted  tooth  resembling  that  of  the  upper  jaw  ;  the 
second,  third  and  fourth  are  two-rooted,  like  the  second  and 
third  of  the  upper  jaw,  which  they  closely  resemble  in  other 
respects. 

The  first  molar  forms  the  carnassial  (fig.  84,  V),  and  with 
the  exception  of  the  canine,  is  much  the  largest  tooth  of  the 
lower  jaw  ;  it  is  a  two-rooted  tooth,  with  a  long  compressed 
bilobed  blade,  and  a  posterior  tuberculated  talon  or  heel.  The 
second  molar  is  much  smaller,  though  likewise  two-rooted,  while 
the  third  molar  is  very  small  and  has  only  a  single  root.  All 
the  teeth  except  the  molars  are  preceded  in  the  young  animal 
by  temporary  milk  teeth.  These  milk  teeth,  though  smaller, 
are  very  similar  to  the  permanent  teeth  by  which  they  are 
ultimately  replaced. 

II.     ENDOSKELETON. 
1.     THE  AXIAL  SKELETON. 

This  includes  the  vertebral  column,  the  skull,  and  the  ribs 
and  sternum. 


378          THE  VERTEBRATE  SKELETON. 

A.     THE  VERTEBRAL  COLUMN. 

This  consists  of  a  series  of  about  forty  vertebrae  arranged 
in  succession  so  that  their  centra  form  a  continuous  rod,  and 
their  neural  arches  a  continuous  tube,  surrounding  a  cavity, 
the  neural  canal. 

The  vertebrae  may  be  readily  divided  into  five  groups  : — 

1.  The  cervical  or  neck  vertebrae. 

2.  The  thoracic  or  chest  vertebrae  which  bear  ribs. 

3.  The  lumbar  vertebrae  which  are  large  and  ribless. 

4.  The  sacral  vertebrae  which  are  fused  with  one  another 
and  united  with  the  pelvis. 

5.  The  caudal  or  tail  vertebrae  which  are  small. 

Except  in  the  sacral  region  the  vertebrae  are  movably 
articulated  to  one  another,  while  their  centra  are  separated 
from  one  another  by  cartilaginous  intervertebral  discs. 

GENERAL  CHARACTERS  OF  A  VERTEBRA. 

Take  as  a  type  the  fourth  lumbar  vertebra.  It  may 
be  compared  to  a  short  tube  whose  inner  surface  is  smooth 
and  regular,  and  whose  outer  surface  is  thickened  and  drawn 
out  in  a  variety  of  ways.  The  basal  part  of  the  vertebra 
is  the  centrum  or  body  which  forms  the  thickened  floor  of 
the  neural  canal.  Its  two  ends  are  slightly  convex  and 
are  formed  by  the  epiphyses,  two  thin  plates  of  bone  which 
are  at  first  altogether  ^distinct  from  the  main  part  of  the  cen- 
trum, but  fuse  with  it  as  the  animal  grows  older ;  its  sides  are 
drawn  out  into  a  pair  of  strong  transverse  processes,  which 
project  forwards,  outwards,  and  slightly  downwards.  The 
neural  arch  forms  the  sides  and  roof  of  the  neural  canal,  and 
at  each  end  just  above  the  centrum  bears  a  pair  of  interver- 
tebral notches  for  the  passage  of  the  spinal  nerves,  the  pos- 
terior notches  being  considerably  deeper  than  the  anterior.  The 
neural  arch  is  drawn  out  into  a  series  of  processes.  Arising 


THE  SKELETON  OF  THE  DOG.   VERTEBRAL  COLUMN.  379 

from  the  centre  of  the  dorsal  surface  is  a  prominent  median 
neural  spine  or  spinous  process,  which  projects  upwards 
and  slightly  forwards  ;  its  anterior  edge  is  vertical,  while  its 
posterior  edge  slopes  gradually.  At  the  two  ends  of  the 
neural  arch  arise  the  two  pairs  of  zygapophyses  or  articula- 
ting surfaces,  which  interlock  with  those  of  the  adjacent 
vertebrae.  The  anterior  or  prezygapophyses  look  inwards, 
and  are  large  and  concave ;  they  are  borne  upon  a  pair  of 
large  blunt  outgrowths  of  the  neural  arch,  the  metapophyses. 
The  posterior  or  postzygapophyses  are  slightly  convex  and 
look  outwards  and  downwards ;  they  are  borne  upon  back- 
warclly  projecting  outgrowths  of  the  neural  arch.  Lastly 
there  are  a  pair  of  minute  projections  arising  from  the 
posterior  end  of  the  neural  arch,  below  the  postzygapophyses. 
These  are  the  anapophyses.  In  young  individuals  the  de- 
velopment of  all  the  processes  of  the  various  vertebrae  is  less 
marked,  arid  the  epiphyses  are  obviously  distinct. 


FlG.    69.       A,    ATLAS    AND    B,    AXIS    VERTEBRA    OF    A   DOG    (CaillS 

familiaris)  (after  VON  ZITTEL). 


1.  transverse  process  of  atlas. 

2.  vertebrarterial  canal. 

3.  foramen    for    exit    of    spinal 

nerve. 

4.  neural  spine. 

5.  odontoid  process. 


6.  anterior   articulating   surface 

of  centrum. 

7.  centrum. 

8.  transverse  process  of  axis. 

9.  postzygapophysis. 


.380  THE   VERTEBRATE   SKELETON. 

THE  CERVICAL  VERTEBRAE. 

These  are  seven  in  number,  as  in  almost  all  mammals. 
They  are  characterised  by  the  fact  that  they  have  small  ribs 
fused  with  them,  forming  transverse  processes  perforated  by 
canals  through  which  the  vertebral  arteries  run. 

The  first,  or  atlas  vertebra  (fig.  69,  A),  differs  much  from 
all  the  others  ;  it  is  drawn  out  into  a  pair  of  wide  wing-like 
transverse  processes  (fig.  69,  A,  1),  and  forms  a  ring  surround- 
ing a  large  cavity.  This  cavity  is  during  life  divided  into 
two  parts  by  a  transverse  ligament ;  the  upper  cavity  is  the 
true  neural  canal,  while  the  lower  lodges  the  odontoid  pro- 
cess of  the  second  vertebra,  which  is  the  detached  centrum 
of  the  atlas.  The  neural  arch  is  broad  and  regular  ;  it  has 
no  spinous  process,  and  is  perforated  in  front  by  a  pair  of 
foramina  for  the  passage  of  the  first  spinal  nerves.  The  mid- 
ventral  portion  of  the  atlas  is  rather  thick,  and  bears  a  minute 
backwardly-projecting  hypapophysis.  The  bases  of  the  broad 
transverse  processes  .are  perforated  by  the  vertebrarterial 
canals  (fig.  69,  A,  2).  The  atlas  bears  at  each  end  a  pair  of 
large  articulating  surfaces;  those  at  the  anterior  end  articulate 
with  the  condyles  of  the  skull,  and  are  very  deeply  concave ; 
those  at  the  posterior  end  for  articulation  with  the  axis,  are 
nearly  as  large,  but  are  flattened.  The  atlas  ossifies  from 
three  centres,  one  forming  the  mid-ventral  portion,  the  others 
the  two  halves  of  the  remainder. 

The  second,  or  axis  vertebra  (fig.  69,  B),  also  differs  much 
from  the  other  cervicals.  The  long  and  broad  centrum  has 
a  very  flat  dorsal  surface,  and  is  produced  in  front  into 
the  conical  odontoid  process  (fig.  69,  B,  5),  and  bears  a 
pair  of  very  large  convex  outwardly-directed  surfaces  for  arti- 
culation with  the  atlas.  At  its  posterior  end  it  is  drawn 
out  into  a  pair  of  small  backwardly-directed  spines,  the 
transverse  processes ;  these  are  perforated  at  their  bases  by 
the  vertebrarterial  canals.  The  neural  arch  is  deeply  notched 
in  front  and  behind  for  the  passage  of  the  spinal  nerves,  and 


THE  SKELETON  OF  THE  DOG.   VERTEBRAE.    381 

is  drawn  out  above  into  a  very  long  compressed  neural  spine 
(fig.  69,  B,  4),  which  projects  a  long  way  forwards,  and  behind 
becomes  bifid  and  thickened,  bearing  a  pair  of  flat  downwardly 
directed  postzygapophyses.  In  the  young  animal  the  odontoid 
process  is  readily  seen  to  ossify  from  a  centre  anterior  to  that 
forming  the  anterior  epiphysis  of  the  axis. 

The  remaining  five  cervical  vertebrae,  the  third  to  the 
seventh  inclusive,  have  rather  flattened  wide  centra,  obliquely 
truncated  at  either  end.  The  neural  spine  progressively  increases 
in  size  as  the  vertebrae  are  followed  back.  The  transverse 
processes  vary  considerably  ;  those  of  the  third  are  divided 
into  a  thicker  backwardly-,  and  a  more  slender  forwardly- 
projecting  portion  ;  those  of  the  fourth  and  fifth  mainly  extend 
downwards,  and  that  of  the  sixth  is  divided  into  a  horizontal 
portion  and  a  downwardly-projecting  inferior  lamella.  All 
the  cervical  vertebrae  except  the  seventh  have  the  bases  of  the 
transverse  processes  perforated  by  the  vertebrarterial  canals. 
The  prezygapophyses  in  each  case  look  upwards  and  slightly 
inwards,  while  the  postzygapophyses  look  downwards  and 
slightly  outwards. 

THE  THORACIC  VERTEBRAE. 

The  thoracic  vertebrae  are  twelve  or  thirteen  in  number, 
and  all  bear  movably  articulated  ribs.  As  a  group  they  are 
characterised  by  their  comparative  shortness,  and  in  the  case 
of  the  first  eight  or  nine  by  the  great  length  of  the  back- 
wardly-sloping  neural  spine.  The  posterior  thoracic  vertebrae 
approach  in  character  the  succeeding  lumbar  vertebrae. 

As  type  of  the  anterior  thoracic  vertebrae,  take  any  one 
between  the  second  and  sixth  inclusive.  The  centrum  is  short, 
and  has  its  terminations  vertically  truncated.  At  the  top  of 
the  centrum,  at  both  anterior  and  posterior  ends  on  each  side, 
is  a  demi-facet  (fig.  70,  A,  4),  which,  together  with  that  on  the 
adjacent  vertebra,  forms  an  articulating  surface  for  the  capitu- 
lum  of  the  rib.  The  neural  arch  is  small  and  deeply  notched 


382 


THE  VERTEBRATE  SKELETON. 


behind  for  the  passage  of  the  spinal  nerve.  It  is  drawn  out 
above  into  a  very  long  neural  spine  (fig.  70,  A,  1),  whose  base 
extends  back  over  the  succeeding  vertebra  and  bears  the  down- 
wardly-directed postzygapophyses  (fig.  70,  A,  6).  The  summit 
of  the  neural  arch  is  deeply  notched  in  front,  and  on  each  side 
of  the  notch  are  the  prezygapophyses,  which  look  almost  ver- 
tically upwards.  The  transverse  processes  are  short  and  blunt, 
and  are  flattened  below  (fig.  70,  A,  3)  for  the  articulation  of 
the  tubercula  of  the  ribs. 


B 


FlG.    70.        A,    SECOND    THORACIC,    AND    B,    SECOND    LUMBAR   VERTEBRA    OF    A 

DOG  (Cants  familiaris)  SEEN  FROM  THE  RIGHT  SIDE  (after  VON  ZITTEL). 


1.  neural  spine.  4. 

2.  centrum. 

3.  transverse  process  bearing  in         5. 

A  the  facet  for  articulation         6. 
with  the  tuberculum  of  the 
rib. 


facet  for  articulation  with  the 

capitulum  of  the  rib. 
metapophysis. 
postzygapophysis. 


The  posterior  three  or  four  thoracic  vertebrae  differ  much 
from  the  others.  The  centra  are  longer,  the  neural  spines  short 
and  not  directed  backwards,  the  articular  facets  for  the  heads 
of  the  ribs  are  confined  to  the  anterior  end  of  the  centrum  of 
each  vertebra,  not  overlapping  on  to  the  preceding  vertebra. 
The  transverse  processes  are  small  and  irregular,  and  nieta- 
pophyses  and  anapophyses  are  developed.  The  prezygapophyses 


THE  SKELETON  OF  THE  DOG.   THE  VERTEBRAE.  383 

also  look  more  inwards,  and  the  postzygapophyses  more  out- 
wards than  in  the  more  typical  thoracic  vertebrae. 

THE  LUMBAR  VERTEBRAE. 

The  lumbar  vertebrae  are  seven  in  number,  and  their 
general  characteristics  have  been  already  described.  As  a 
group  they  are  characterised  by  their  large  size,  and  the  great 
development  of  the  transverse  processes,  inetapophyses  and 
neural  spines. 

THE  SACRAL  VERTEBRAE. 

Three  vertebrae  are  commonly  found  fused  together,  forming 
the  sacrum ;  the  divisions  between  the  three  being  indicated 
by  the  foramina  for  the  exit  of  the  spinal  nerves. 

Of  these  three  vertebrae,  the  first  is  much  the  largest, 
and  is  firmly  united  to  the  ilium  on  each  side  by  a  structure 
formed  by  the  transverse  processes  and  expanded  ribs.  In  the 
adult  this  structure  forms  one  continuous  mass,  but  in  the 
young  animal  a  ventral  portion  formed  by  the  rib  is  clearly 
distinguishable  from  a  dorsal  portion  formed  by  the  transverse 
process.  All  three  have  low  neural  spines.  The  anterior 
sacral  vertebra  bears  a  large  pair  of  prezygapophyses,  while 
the  posterior  one  bears  a  small  pair  of  postzygapophyses. 

THE  CAUDAL  VERTEBRAE. 

The  caudal  vertebrae  are  about  nineteen  in  number. 
The  earlier  ones  have  well-developed  neural  arches,  transverse 
processes,  and  zygapophyses,  but  as  the  vertebrae  are  followed 
back  they  gradually  lose  all  their  processes,  and  the  neural  arch 
as  well,  becoming  at  about  the  thirteenth  from  the  end  reduced 
to  simple  cylindrical  centra. 

B.     THE  SKULL. 

The  skull  consists  of  the  following  three  parts  :  (a)  the 
cranium,  with  which  are  included  the  skeletal  s»fpports  of  the 
various  special  sense  organs,  and  the  bones  of  the  face  and 
upper  jaw  ;  (6)  the  lower  jaw  or  mandible,  which  is  movably 
articulated  to  the  cranium,  and  (c)  the  hyoid. 


384          THE  VERTEBRATE  SKELETON. 

(a)     THE  CRANIUM. 

The  cranium  is  a  compact  bony  box,  forming  the  anterior 
expanded  portion  of  the  axial  skeleton.  It  has  a  longitu- 
dinal axis,  the  craniofacial  axis  around  which  the  various 
parts  are  arranged,  and  this  axis  is  a  direct  continuation  of 
that  of  the  vertebral  column.  Similarly  the  cavity  of  the 
cranium  is  a  direct  continuation  of  the  spinal  canal.  The 
posterior  part  of  the  craniofacial  axis,  which  has  relation^ 
only  with  the  cranium,  is  called  the  basicranial  axis. 

In  the  dog  as  in  the  other  types  previously  described,  the 
skull  in  its  earliest  stages  is  cartilaginous,  containing  no  bone. 
In  the  adult,  however,  the  cartilage  is  to  a  great  extent 
replaced  by  bone,  and  in  addition  to  this  cartilage  bone, 
membrane  bone  is  largely  developed,  .and  intimately  united 
with  the  cartilage  bone  to  form  one  complete  whole. 

In  the  description  of  the  dog's  skeleton,  as  in  those  of  the 
previous  types,  the  names  of  the  membrane  bones  are  printed 
in  italics,  while  those  of  the  cartilage  bones  are  printed  in 
thick  type. 

Most  of  the  numerous  foramina  perforating  the  skull 
walls  will  be  described  after  the  bones  have,  been  dealt  with. 

For  purposes  of  description  the  cranium  may  be  further 
subdivided  into : — 

1 .  The  cranium  proper  or  brain  case. 

2.  The  sense  capsules. 

3.  The  upper  jaw. 

1.     THE  CRANIUM  PROPER  OR  BRAIN  CASE. 

Taking  the  membrane  and  cartilage  bones  together,  they 
are  seen  to  be  more  or  less  arranged  in  three  segments,  which 
however  must  not  be  regarded  as  homologous  with  the  seg- 
ments forming  the  vertebral  column. 

The  occipital  segment  is  the  most  posterior  of  the  three, 
and  consists  of  four  cartilage  bones,  which  in  the  adult  are 
commonly  completely  fused  together.  They  surround  the  great 


THE  SKELETON  OF  THE  DOG.   THE  SKULL. 


385 


FIG.  71,     DIAGRAM  OF  THE  RELATIONS  OF  THE  PRINCIPAL  BONES  IN  THE 
MAMMALIAN  SKULL  (modified  after  FLOWER). 

Cartilage  is  dotted.     Cartilage  bones  are  marked  by  dots  and  dashes, 
membrane  bones  are  left  white. 


1. 

basi-occipital. 

15. 

mesethmoid. 

2. 

exoccipital. 

16. 

vomer. 

3. 

supra-occipital. 

17. 

pterygoid. 

4. 

basisphenoid. 

18. 

palatine. 

5. 

alisphenoid. 

19. 

maxilla. 

6. 

parietal. 

20. 

premaxilla. 

7. 

presphenoid. 

21. 

squamosal. 

8. 

orbitosphenoid. 

22. 

mandible. 

9. 

frontal. 

23. 

tympano-hyal. 

10. 

periotic,    immediately    below 

24. 

stylo-hyal. 

which  is  the  tympanic. 

25. 

epi-hyal. 

11. 

lachrymal. 

26. 

basi-hyal.     Between  this  and 

12. 

ethmo-turbinal. 

the  epi-hyal  is  the  cerato-hyal. 

13. 

maxillo-turbinal. 

27. 

thyro-hyal. 

14. 

nasal. 

28. 

jugal. 

Nerve  exits  are  indicated  by  Eoman  numerals. 


R. 


25 


386          THE  VERTEBRATE  SKELETON. 

foramen  magnum  (fig.  75,  2)  through  which  the  brain  and 
spinal  cord  communicate.  Forming  the  lower  margin  of  the 
foramen  magnum  is  a  large  flat  unpaired  bone,  the  basi- 
occipital  (fig.  75,  5).  Above  this  on  each  side  are  the  ex- 
OCCipitals,  whose  sides  are  drawn  out  into  a  pair  of  down- 
wardly-directed paroccipital  processes,  which  are  applied 
to  the  tympanic  bullae1.  The  inner  side  of  each  exoccipital  is 
converted  into  the  large  rounded  occipital  condyle  (fig.  72, 
13)  by  which  the  skull  articulates  with  the  atlas  vertebra.  The 
dorsal  boundary  of  the  foramen  magnum  is  formed  by  a  large 
unpaired  flat  bone,  the  supra-occipital  (figs.  72  and  75,  1), 
which  is  continuous  with  a  small  bone,  the  interparietal,  pro- 
longed forwards  between  the  parietal  bones  of  the  next  segment. 
In  old  animals  the  interparietal  forms  the  hind  part  of  a 
prominent  ridge  running  along  the  mid-dorsal  surface  of  the 
skull  and  called  the  sagittal  crest,  while  the  junction  line  of 
the  occipital  and  parietal  segments  forms  a  prominent  occi- 
pital crest. 

The  plane  in  which  the  bones  of  the  occipital  segment  lie 
is  called  the  occipital  plane ;  the  angle  that  it  makes  with  the 
basicranial  axis  varies  much  in  different  mammals. 

The  parietal  segment  consists  of  both  cartilage  and 
membrane  bones.  It  is  formed  of  five  bones,  which  are  in 
contact  with  those  of  the  occipital  segment  on  the  dorsal  and 
ventral  surfaces,  while  laterally  they  are  separated  by  the  inter- 
position of  the  auditory  bones,  and  to  some  extent  of  the  squa- 
mosal.  The  basisphenoid  (fig.  75,  6),  an  unpaired  bone 
forming  the  ventral  member  of  this  segment,  is  the  direct 
continuation  of  the  basi-occipital.  It  tapers  anteriorly,  but  is 
rather  deep  vertically,  its  upper  or  dorsal  surface  bearing  a 
depression,  the  sella  turcica,  which  lodges  the  pituitary  body 
of  the  brain.  From  the  sides  of  the  basisphenoid  arise  the 
alisphenoids  (fig.  75,  11)  a  pair  of  bones  of  irregular  shape 
generally  described  as  wing-like  ;  each  gives  off  from  its  lower 
1  See  p.  392. 


THE  SKELETON  OF  THE  DOG.   THE  SKULL. 


387 


19      3 


FIG. 


1. 
2. 

3. 
4. 
5. 
6. 

7. 

8. 

9. 
10. 
11. 
12. 
18. 
1-1. 
15. 
IB. 
17. 


27 


72.     VEBTICAL  LONGITUDINAL  SECTION  TAKEN  A  LITTLE  TO  THE  LEFT 

OF    THE    MIDDLE    LINE    THROUGH    THE    SKULL     OF    A    DOG    (Cants 

liaris)  x  £ .     (Camb.  Mus.) 


supra-occipital. 

interparietal. 

parietal. 

frontal. 

cribriform  plate. 

nasal. 

mesethmoid. 

maxilla. 

vomer. 

ethmo-turbinal. 

maxillo-turbinal. 

premaxilla. 

occipital  condyle. 

basi-occipital. 

tympanic  bulla. 

basisphenoid. 

pterygoid. 


18.  palatine. 

19.  alisphenoid. 

20.  internal  auditory  meatus. 

21.  tentorium. 

22.  foramen  lacerum  posterius. 

23.  floccular  fossa. 

24.  coronoid  process. 

25.  condyle. 

26.  angle. 

27.  mandibular  symphysis. 

28.  inferior  dental  foramen. 

29.  stylo-hyal. 

30.  epi-hyal. 

31.  cerato-hyal. 

32.  basi-hyal. 

33.  thyro-hyal. 

XII.     condylar  foramen. 


25—2 


388          THE  VERTEBRATE  SKELETON. 

surface  a  pterygoid  plate,  which  is  united  in  front  with  the 
palatine,  and  below  with  the  pterygoid.  The  alisphenoids  are 
united  above  with  a  pair  of  large  nearly  square  bones,  the 
parietals  (fig.  73,  2),  which  meet  one  another  in  the  mid-dorsal 
line.  The  line  of  junction  is  frequently  drawn  out  into  a  strong 
ridge,  which  forms  the  anterior  part  of  the  sagittal  crest. 

The  frontal  segment,  which  surrounds  the  anterior  part 
of  the  brain,  is  closely  connected  along  almost  its  whole 
posterior  border  with  the  parietal  segment. 

Its  base  is  formed  by  the  presphenoid  (fig.  75,  12),  a 
very  deep  unpaired  bone,  narrow  and  compressed  ventrally, 
and  with  an  irregular  dorsal  surface.  The  presphenoid  is 
continuous  with  a  second  pair  of  wing-like  bones,  the  orbito- 
sphenoids.  Each  orbitosphenoid  meets  the  alisphenoid 
behind,  but  the  relations  of  the  parts  in  this  region  are 
somewhat  obscured  by  a  number  of  large  foramina  piercing 
the  bones,  and  also  by  an  irregular  vacuity,  the  foramen 
lacerum  anterius  or  sphenoidal  fissure,  which  lies  between 
the  orbitosphenoid  and  alisphenoid,  separating  the  lateral  parts 
of  the  parietal  and  frontal  segments,  in  the  same  way  as  the 
space  occupied  by  the  auditory  bones  separates  the  lateral 
parts  of  the  occipital  and  parietal  segments.  The  orbito- 
sphenoids  pass  obliquely  forwards  and  upwards,  and  are  united 
above  with  a  second  pair  of  large  membrane  bones,  thefrontals 
(fig.  73,  3).  The  outer  side  of  each  frontal  is  drawn  out  into 
a  rather  prominent  rounded  postorbital  process  (fig.  73,  10), 
from  which  a  ridge  converges  backwards  to  meet  the  sagittal 
crest.  The  anterior  part  of  the  frontal  is  produced  to  form 
the  long  nasal  process,  which  is  wedged  in  between  the  nasal 
and  maxilla. 

The  cranial  cavity  is  continuous  in  front  with  the  nasal  or 
olfactory  cavities,  but  the  passage  is  partially  closed  by  a 
screen  of  bone,  the  cribriform  plate  (fig.  72,  5),  which  is 
placed  obliquely  across  the  anterior  end  of  the  cranial  cavity, 
and  is  perforated  by  a  number  of  holes  through  which  the 


THE  SKELETON  OF  THE  DOG.   THE  SKULL.    389 


FIG.  73.     DORSAL  VIEW  OF  THE  CRANIUM  OF  A  DOG  (Canis  fami- 
liar  is)  x  •§. 


1.  supra-occipital. 

2.  parietal. 

3.  frontal. 

4.  nasal. 

•5.  maxilla  (facial  portion). 

6.  premaxilla. 

7.  squamosal. 

8.  jugal. 


10.  postorbital  process  of  frontal. 

11.  infra-orbital  foramen.      % 

12.  anterior  palatine  foramen. 

13.  lachrymal  foramen. 
i  1.     first  incisor. 

c.     canine. 

pm  4.     fourth  premolar. 


390  THE  VERTEBRATE  SKELETON. 

olfactory  nerves  pass.  The  plane  of  the  cribriform  plate  is 
called  the  ethmoidal  plane,  and  as  was  the  case  also  with 
the  occipital  plane,  the  angle  that  it  makes  with  the  basi- 
cranial  axis  varies  much  in  different  mammals,  and  is  of 
importance.  The  olfactory  fossa  in  which  lie  the  olfactory 
lobes  of  the  brain,  is  partially  separated  from  the  cerebral 
fossa,  or  cavity  occupied  by  the  cerebral  hemispheres,  by 
ridges  on  the  orbitosphenoids  and  frontals.  The  presphenoid 
is  connected  in  front  with  a  vertical  plate  formed  partly  of  bone, 
partly  of  unossified  cartilage;  this  plate,  the  mesethmoid 
(fig.  72,  7),  separates  the  two  olfactory  cavities  which  lodge 
the  olfactory  organs.  Its  anterior  end  always  remains  un- 
ossified, and  forms  the  septal  cartilage  of  the  nose. 

The  brain  case  may  then,  to  use  the  words  of  Sir  W.  H. 
Flower,  be  described  as  a  tube  dilated  in  the  middle  'and  com- 
posed of  three  bony  rings  or  segments,  with  an  aperture  at  each 

end,  and  a  fissure  or  space  at  the  sides  between  each  of  them. 

i 
2.     THE  SENSE  CAPSULES. 

Each  of  the  three  special  sense  organs,  of  hearing,  of  sight, 
and  of  smell,  is  in  the  embryo  provided  with  a  cartilaginous 
or  membranous  protecting  capsule ;  and  two  of  these,  the 
auditory  and  olfactory  capsules,  become  afterwards  more  or 
less  ossified,  and  intimately  related  to  the  cranium  proper. 

(1)     Bones  in  relation  to  the  Auditory  capsules. 

These  bones  lie  on  each  side  wedged  into  the  vacuity  be- 
tween the  lateral  parts  of  the  occipital  and  parietal  segments ; 
they  are  three  in  number,  the  periotic,  the  tympanic  and  the 
squamosal. 

The  periotic  is  the  most  important  of  them,  as  it  replaces 
the  cartilaginous  auditory  capsule  of  the  embryo,  and  encloses 
the  essential  organ  of  hearing.  It  commences  to  ossify 
from  three  centres  corresponding  to  the  pro-otic,  epi-otic  and 
opisthotic  of  lower  skulls,  such  as  those  of  the  Turtle  and 
Crocodile. 


THE  SKELETON  OF  THE  DOG.   THE  SKULL. 


391 


These  ossifications  however  very  early  combine  to  form  a 
single  bone,  the  periotic,  which  nevertheless  consists  of  two 


FIG.  74. 


DIAGRAM  OF  THE  MAMMALIAN  TYMPANIC  CAVITY  AND  ASSOCIATED 
PARTS  (modified  from  LLOYD  MORGAN). 


1.  external  auditory  meatus. 

2.  tympanic  membrane. 

3.  malleus. 

4.  incus. 

5.  lenticular. 

6.  stapes. 


7.  fenestra  ovalis. 

8.  fenestra  rotunda. 

9.  Eustachian  tube. 

10.  cavity  occupied  by  the  cochlea. 

11.  cavity  occupied  by  the  mem- 

branous labyrinth. 


portions,  the  petrous  and  the  mastoid,  differing  considerably 
from  one  another. 

The  petrous  portion  lies  dorsally  and  anteriorly,  and  is 
much  the  more  important  of  the  two,  as  it  encloses  the 
essential  part  of  the  auditory  organ.  It  forms  an  irregular 
mass  of  hard  dense  bone,  projecting  into  the  cranial  cavity, 
and  does  not  appear  on  the  external  surface  at  all.  The 
mastoid  portion  lies  ventrally  and  posteriorly,  is  smaller, 
and  formed  of  less  dense  bone  than  is  the  petrous  portion, 
from  which  it  differs  also  in  the  fact  that  it  appears  on  the 
surface  of  the  skull,  just  external  to  the  exoccipital.  The 
petrous  portion  bears  a  ridge,  which  together  with  a  ridge 


392          THE  VERTEBRATE  SKELETON. 

on  the  supra-occipital,  and  the  tentorium  (fig.  72,  21),  a 
transverse  fold  of  the  dura  mater1,  separates  the  large  cerebral 
fossa  from  the  cerebellar  fossa,  which  is  much  smaller  than 
the  cerebral  fossa  and  lies  behind  and  partly  beneath  it.  The 
plane  of  the  tentorium  is  called  the  tentorial  plane,  and  the 
angles  that  it  makes  with  the  basicranial  axis  and  with  the 
occipital  and  ethmoidal  planes  vary  much  in  different  mammals. 

The  periotic  has  its  inner  surface  marked  by  important 
depressions,  while  both  inner  and  outer  surfaces  are  pierced 
by  foramina.  At  about  the  middle  of  its  inner  surface  are 
seen  two  deep  pits,  one  lying  immediately  above  the  other. 
Of  these  the  more  ventral  is  a  foramen,  the  internal  audi- 
tory meatus  (fig.  72,  20),  through  which  the  Vllth  (facial) 
and  Vlllth  (auditory)  nerves  leave  the  cranial  cavity,  the 
facial  nerve  passing  through  the  bone  and  afterwards  leaving 
the  skull  by  the  stylomastoid  foramen  (fig.  75,  VII),  while 
the  auditory  passes  to  the  inner  ear.  The  more  dorsal  of  the 
two  pits  is  not  a  foramen  but  the  floccular  fossa  (fig.  72,  23) 
which  lodges  the  floccular  lobe  of  the  cerebellum.  In  some 
skulls  another  wide  and  shallow  but  fairly  prominent  depres- 
sion is  seen  dorsal  to  and  slightly  behind  the  floccular  fossa, 
this  also  lodges  part  of  the  cerebellum.  Behind  the  internal 
auditory  meatus,  between  the  periotic  and  exoccipital  is  seen 
the  internal  opening  of  the  foramen  lacerum  posterius 
(fig.  72,  22).  The  shape  of  this  opening  varies.  The  ventro- 
aiiterior  border  of  the  periotic  is  marked  by  a  deep  notch,  the 
sides  of  which  sometimes  unite,  converting  it  into  a  foramen. 

On  the  outer  -side  of  the  periotic,  and  clearly  seen  only 
after  the  removal  of  the  tympanic,  are  two  holes,  the  fenestra 
ovalis  and  the  fenestra  rotunda. 

The  tympanic  (figs.  72,  15  and  75,  4)  is  a  greatly  expanded 
boat-shaped  bone,  which  forms  the  auditory  bulla  and  lies 
immediately  ventral  to  the  periotic ;  it  is  separated  from  the 

1  The  dura  mater  is  a  membrane  which  lines  the  cranial  cavity  and 
is  formed  of  tough  connective  tissue. 


THE  SKELETON  OF  THE  DOG.   THE  SKULL.    393 

periotic  by  the  tympanic  cavity  into  which  the  fenestra 
rotunda  and  the  fenestra  ovalis  open. 

There  are  several  other  openings  into  the  tympanic  cavity. 

(a)  On  the  external  surface  is  a  large  oval  opening,  the 
external  auditory  meatus  bounded  by  a  thickened  rim. 

(6)  Into  the  outer  and  anterior  part  of  the  cavity  the 
outer  end  of  the  Eustachian  tube  opens;  while  the  inner 
end  passes  through  a  foramen  (fig.  75,  22)  just  external  to  the 
foramen  lacerum  medium,  on  its  way  to  open  into  the  pharynx. 

(c)  The  internal  carotid  artery  also  enters  the  tympanic 
cavity  by  a  canal  which  commences  in  the  foramen  lacerum 
posterius,  and  passes  forwards  to  open  on  the  inner  side  of  the 
bulla.  The  artery  then  passes  forwards,  and  barely  appearing 
on  the  ventral  surface  of  the  cranium,  enters  the  brain  cavity 
through  the  foramen  lacerum  medium  (fig.  75,  9). 

Immediately  behind  the  tympanic,  between  it  and  the 
mastoid  process  of  the  periotic  and  the  paroccipital  process  of 
the  exoccipital  is  the  stylomastoid  foramen  (fig.  75,  VIII). 

Within  the  tympanic  cavity  are  four  small  bones,  the 
auditory  ossicles  (cp.  fig.  74),  called  respectively  the  mal- 
leus, incus,  lenticular  and  stapes;  these  together  form  a 
chain  extending  from  the  fenestra  ovalis  to  the  tympanic 
membrane. 

The  malleus  has  a  somewhat  rounded  head  (fig.  100,  B,  1) 
which  articulates  with  the  incus,  while  the  other  end  of  the 
bone  is  drawn  out  into  a  long  process,  the  manubrium, 
which  lies  in  relation  to  the  tympanic  membrane.  The  head 
is  also  more  or  less  connected  by  a  thin  plate  of  bone,  the 
lamella,  to  another  outgrowth,  the  processus  longus.  The 
incus  (fig.  100,  B,  3)  is  somewhat  anvil-shaped,  and  is  drawn 
out  into  a  process  which  is  connected  with  the  lenticular,  a 
nodule  of  bone  interposed  between  the  incus  and  the  stapes, 
with  which  it  early  becomes  united.  The  stapes  (fig.  100,  B,  2) 
is  stirrup-shaped,  consisting  of  a  basal  portion  from  which 
arise  two  crura,  which  meet  and  enclose  a  space,  the  canal. 


394  THE  VERTEBRATE  SKELETON. 

The  squamosal  (fig.  73,  7)  is  a  large  bone  occupying  much 
of  the  side  wall  of  the  cranial  cavity,  and  articulating  above 
with  the  parietal,  and  behind  with  the  supra-occipital,  while 
in  front  it  overlaps  the  frontal  and  alisphenoid.  But  though  it 
occupies  so  large  a  space  on  the  outer  wall,  it  forms  very 
little  of  the  internal  wall  of  the  skull,  but  is  really  like  a  bony 
plate  attached  to  the  outer  surface  of  the  cranial  wall.  The 
squamosal  is  drawn  out  into  a  strong  forward ly-directed  zygo- 
matic  process  which  meets  the  jugal  or  malar.  The  ventral 
side  of  the  zygomatic  process  is  hollowed  out,  forming  the 
glenoid  fossa  (fig.  75,  8),  a  smooth  laterally  elongated  surface 
with  which  the  lower  jaw  articulates,  while  the  hinder  edge  of 
the  glenoid  fossa  is  drawn  out  into  a  rounded  postglenoid 
process  (fig.  75,  23).  The  articulation  is  such  as  to  allow 
but  little  lateral  play  of  the  lower  jaw. 

(2)  Bones  in  relation  to  the  Optic  capsules. 

The  only  bone  developed  in  relation  to  the  optic  capsule 
on  each  side  is  the  lachrymal.  This  is  a  small  membrane 
bone  lying  between  the  frontal  and  palatine  behind,  and  the 
maxilla  and  jugal  in  front.  It  is  perforated  by  a  prominent 
lachrymal  foramen  (fig.  73,  13)  which  opens  within  the 
orbit. 

(3)  Bones  in  relation  to  the  Olfactory  capsules. 

In  connection  with  the  olfactory  capsules,  five  pairs  of 
bones  are  developed,  two  pairs  being  membrane  bones,  and 
three  pairs  cartilage  bones. 

Of  membrane  bones,  the  nasals  (fig.  73,  4)  are  a  pair  of 
long  narrow  bones,  lying  closely  side  by  side,  and  forming 
the  main  part  of  the  roof  of  the  olfactory  chamber.  Their 
posterior  ends  overlap  the  froritals,  and  the  outer  margin  of 
each  is  in  contact  with  the  nasal  process  of  the  frontal,  and 
with  the  maxilla  and  premaxilla. 

Lying  immediately  ventral  to  the  nasals,  and  on  each 
side  of  the  perpendicular  mesethmoid,  are  the  ethmoid  or 


THE  SKELETON  OF  THE  DOG.   THE  SKULL.    395 

turbinal  bones,  which  have  a  curious  character,  being  formed 
of  a  number  of  delicate  plates  intimately  folded  on  one 
another.  The  posterior  pair  of  these  bones,  the  ethmo- 
turbinals  (fig.  72,  10),  are  the  larger,  and  form  a  mass  of 
intricately  folded  lamellae  attached  behind  to  the  cribriform 
plate,  and  passing  laterally  into  two  thin  plates  of  bone, 
which  abut  on  the  maxillae.  The  uppermost  lamella  of  each 
ethmo-turbinal  is  larger  than  the  others  and  more  distinct. 
It  is  sometimes  distinguished  as  the  naso -turbinal,  and  forms 
an  imperfect  lower  boundary  to  a  canal,  which  is  bounded 
above  by  the  nasals.  In  front  of  and  somewhat  below  the 
ethmo-turbinals,  lie  another  pair  of  bones  of  similar  character, 
the  maxillo-turbinals  (fig.  72,  11). 

The  last  bone  to  be  mentioned  in  connection  with  the 
olfactory  capsules  is  a  membrane  bone,  the  vomer  (fig.  72,  9). 
This  is  a  slender  vertically-placed  bone,  whose  anterior  part  lies 
between  the  maxillo-turbinals,  while  behind  it  extends  beyond 
the  mesethmoid,  so  as  to  underlie  the  anterior  part  of  the  pre- 
sphenoid.  The  anterior  part  of  the  vomer  forms  a  kind  of 
trough,  while  further  back  in  the  region  of  the  ethmo-turbinals 
it  sends  out  a  pair  of  strong  lateral  plates,  each  of  which, 
passing  below  the  ethmo-turbinal,  joins  the  side  wall  of  the 
nasal  cavity,  and  forms  a  partition  dividing  the  nasal 
cavity  into  a  lower  narial  passage  and  an  upper  olfactory 
chamber. 

THE  JAWS. 

In  the  embryo  both  upper  and  lower  jaws  are  formed  of 
cartilaginous  bars,  but  in  the  adult  not  only  has  the  cartilage 
entirely  disappeared,  but  even  cartilage  bone  is  absent,  the 
jaws  being  formed  of  membrane  bone. 

3.     THE  UPPER  JAW. 

The  bones  of  the  upper  jaw  are  closely  connected  with 
those  of  the  cranium  proper  and  olfactory  capsules.  The  most 


396 


THE  VERTEBRATE  SKELETON. 


—  22 


FIG.  75.     VENTRAL  VIEW  OF  THE  CRANIUM  OF  A  DOG  (Canisfami- 
liaris)  x  f .     (Camb.  Mus. ) 

anterior  opening  o'f  carotid 
canal. 

10.  postglenoid  foramen. 

11.  alisphenoid. 

12.  presphenoid. 

13.  vomer. 


1.  supra-occipital. 

2.  foramen  magnum. 

3.  occipital  condyle. 

4.  tympanic  bulla. 

5.  basi-occipital. 

6.  basisphenoid. 


7.  external  auditory  meatus.  14.     jugal. 

8.  glenoid  fossa.  15.     pterygoid. 

9.  foramen  lacerum  medium  and       16.     palatal  process  of  palatine. 


THE  SKELETON  OF  THE  DOG.   THE  SKULL.    397 

17.  maxilla  (palatal  portion).  V2.     foramen  rotundum. 

18.  posterior  palatine  foramina.  V3.     foramen  ovale. 

19.  anterior  palatine  foramen.  VII.     stylomastoid  foramen. 

20.  premaxilla.  IX,  X,  XI.     foramen  lacerum  pos- 

21.  alisphenoid  canal.  terius. 

22.  Eustachian  foramen.  XII.     condylar  foramen. 

23.  postglenoid  process  of  squa-  i  2.     second  incisor. 

mosal.  c.     canine. 

II.  optic  foramen.  pml,  pm4.     first  and  fourth  pre- 

III,  IV,  Vj,  VI.  foramen  lacerum  molars. 

an  terius.  in  1.     first  molar. 

posterior  of  them  is  the  pterygoid  (fig.  75,  15),  a  thin  verti- 
cally placed  plate  of  bone,  which  articulates  above  with  the 
basisphenoid,  the  presphenoid,  and  the  strong  pterygoid  pro- 
cess of  the  alisphenoid.  The  ventral  end  of  the  pterygoid 
is  drawn  out  into  a  small  backwardly-p rejecting  hamular 
process.  In  front  the  pterygoid  articulates  with  the  palatine, 
a  much  larger  bone,  consisting  of  (1)  a  vertical  portion,  which 
passes  up  to  meet  the  orbitosphenoid  and  frontal,  and  sends 
inwards  a  plate  which  meets  the  presphenoid  and  vomer,  form- 
ing much  of  the  roof  of  the  posterior  part  of  the  narial  passage; 
and  (2)  a  strong  horizontal  portion,  the  palatal  process  (fig. 
75,  16),  which  passes  inwards  and  meets  its  fellow  in  the 
middle  line,  forming  the  posterior  part  of  the  bridge  of  bone 
supporting  the  hard  palate.  The  palatal  process  is  continuous 
in  front,  with  a  large  bone,  the  maxilla,  which,  like  the  pala- 
tine, consists  of  vertical  and  horizontal  portions.  The  vertical, 
or  facial  portion  (fig.  73,  5),  i&  the  largest,  and  constitutes 
the  main  part  of  the  side  of  the  face  in  front  of  the  orbit,  form- 
ing also  the  chief  part  of  the  outer  wall  of  the  nasal  cavity. 
It  is  continuous  in  front  with  the  premaxilla,  above  with  the 
nasal  and  frontal,  and  behind  with  the  lachrymal,  jugal,  and 
palatine.  The  horizontal,  or  palatal  portion  (fig.  75,  17), 
forms  the  anterior  part  of  the  bony  plate  supporting  the  hard 
palate,  and  meets  its  fellow  in  a  long  straight  symphysis.  The 
junction  line  between  the  palatal  and  facial  portions  is  called 


398  THE   VERTEBRATE   SKELETON. 

the  alveolar  border,  and  along  it  are  attached  the  canine, 
premolar,  and  molar  teeth. 

The  anterior  part  of  the  upper  jaw  on  each  side  is  formed 
by  a  small  bone,  the  premaxilla,  which  bears  the  incisor  teeth. 
It,  like  the  maxilla,  has  a  palatal  portion  (fig.  75,  20),  which 
meets  its  fellow  in  the  middle  line,  and  an  ascending  portion, 
which  passes  backwards  as  the  nasal  process, 'tapering  regu- 
larly and  lying  between  the  nasal  and  the  maxilla.  The  two 
premaxillae  form  the  outer  and  lower  borders  of  the  anterior 
nares.  The  last  bone  to  be  mentioned  in  connection  with  the 
upper  jaw  and  face  is  the  jugal  or  malar  (figs.  73,  8,  and  75,  14), 
a  strong  bone  which  forms  the  anterior  half  of  the  zygomatic 
arch.  It  is  firmly  united  in  front  to  the  maxilla,  and  behind 
meets  the  zygomatic  process  of  the  squamosal,  being  drawn 
out  dorsally  into  a  short  postorbital  process  at  the  point  of 
meeting.  This  process  lies  immediately  below  the  postorbital 
process  of  the  frontal,  and  if  the  two  met,  as  they  do  in  some 
mammals,  they  would  partially  shut  off  the  orbit  from  a  larger 
posterior  cavity,  the  temporal  fossa.  In  the  living  animal  a 
ligament  unites  the  two  postorbital  processes. 

(b)     THE  LOWER  JAW  OR  MANDIBLE. 

This  consists  of  two  elongated  symmetrical  halves,  the 
rami,  which  are  united  to  one  another  at  the  median 
symphysis  in  front,  while  behind  they  diverge  considerably, 
and  each  articulates  with  the  glenoid  surface  of  the  corre- 
sponding squamosal.  In  young  animals  the  rami  are  united  at 
the  symphysis  by  fibrous  tissue,  but  in  old  animals  they  some- 
times become  fused  together.  The  upper  or  alveolar  border- 
bears  the  teeth,  and  behind  them  is  drawn  out  into  a  high 
laterally  compressed  coronoid  process  (fig.  72,  24),  which  is 
hollowed  on  its  outer  surface.  Immediately  behind  the  coronoid 
process  is  the  transversely  elongated  condyle  (fig.  72,  25), 
which  fits  into  the  glenoid  cavity  in  such  a  way  as  to  allow 
free  up  and  down  movement  of  the  jaw,  with  but  little  rolling 
motion.  The  posterior  end  of  the  jaw  below  the  condyle  forms 


THE  SKELETON  OF  THE  DOG.   THE  SKULL.    399 

a  short  rounded  process,  the  angle  (fig.  72,  26).  Two  promi- 
nent foramina  are  to  be  seen  in  the  lower  jaw.  These  are 
firstly  the  inferior  dental  foramen  (fig.  72,  28),  which  lies 
on  the  inner  surface  below  the  coronoid  process ;  through  it 
an  artery  and  a  branch  of  the  fifth  nerve  enter  to  supply  the 
teeth,  and  secondly  the  mental  foramen,  which  lies  on  the 
outer  side  near  the  anterior  end,  and  through  which  a  branch 
of  the  same  nerve  emerges. 

(c)     THE  HYOID. 

The  Hyoid  of  the  dog  consists  of  a  transverse  median 
piece,  the  basi-hyal1  (fig.  72,  32),  from  which  arise  two  pairs  of 
cornua.  The  anterior  cornu  is  much  the  longer  of  the  two, 
and  consists  principally  of  three  short  separate  ossifications, 
placed  end  to  end  and  called  respectively  the  cerato-hyal1, 
epi-hyal,  and  stylo-hyal.  All  of  them  are  short  rods  of  bone, 
contracted  in  the  middle,  and  expanded  at  the  ends,  where  they 
are  tipped  with  cartilage.  The  cerato-hyal  (fig.  72,  3 1 )  lies  next 
to  the  basi  hyal.  The  stylo-hyal  is  terminated  by  a  much  smaller 
bone,  the  tympano-hyal,  which  lies  in  a  canal  between  the 
tympanic  and  periotic,  and  is  ankylosed  to  the  periotic  just 
to  the  anterior  and  inner  side  of  the  stylomastoid  foramen. 

The  posterior  cornu  of  the  hyoid  is  much  smaller  than 
the  anterior ;  it  consists  of  a  short  bone,  the  thyro-hyal  (fig. 
72,  33),  which  connects  the  basi-hyal  with  the  thyroid  cartilage 
of  the  larynx. 

FORAMINA  OF  THE  SKULL. 

The  foramina,  or  apertures  perforating  the  walls  of  the 
skull,  are  very  numerous,  arid  may  either  be  due  to  holes 
actually  penetrating  the  bone,  or  may  be  small  vacuities 
between  the  margins  of  two  elsewhere  contiguous  bones. 

They  may  be  divided  into  two  groups,  the  first  including 

I.  The  holes  through  which  the  twelve  cranial  nerves 
leave  the  cranial  cavity. 

1  These  are  not  strictly  homologous  with  the  basi-hyal  and  cerato-hyal 
of  the  Dogfish. 


400  THE  VERTEBRATE  SKELETON. 

a.  The  most  anterior  of  these  nerves,  the  olfactory,  leaves 
the  skull  by  a  number  of  small  holes  piercing  the  cribriform 
plate  (fig.  72,  5). 

6.  The  second,  or  optic,  passes  out  by  a  large  hole,  the 
optic  foramen  (fig.  75,  II)  piercing  the  orbitosphenoid.  The 
optic  foramen  is  the  most  anterior  of  the  three  prominent 
holes  seen  within  and  immediately  behind  the  orbit. 

c.  The  third,  fourth,  and  sixth  nerves,  i.e.  those  supplying 
the  eye  muscles,  and  with  them  the  first  or  ophthalmic  branch 
of  the  large  fifth  or  trigeminal  nerve,  pass  out  by  a  large  hole, 
the  foramen  lacerum  anterius  (fig.  75,  III,  IY,  V^VI), 
which,    as    has    been    already    mentioned,    lies    between   the 
orbitosphenoid  and  alisphenoid. 

d.  Immediately  behind  the  foramen  lacerum  anterius,  the 
alisphenoid   is   perforated   by  a   prominent  round    hole,    the 
foramen  rotundum  (fig.  75,  V2),  through  which  the  second 
branch  of  the  trigeminal  nerve  passes  out. 

e.  A  quarter  of  an  inch   further  back  there  is  another 
prominent  hole,  the  foramen   ovale  (fig.    75,  Y3),   through 
which   the  third   branch   of  the  trigeminal  nerve  leaves  the 
cranium. 

f.  The  seventh  or  facial  nerve,    as    already   mentioned, 
leaves   the    cranial    cavity  and  enters  the  auditory  capsule, 
through    an    opening    in    the    periotic    called   the    internal 
auditory  meatus,  while  it  finally  leaves  the  skull  by  the 
stylomastoid   foramen  (fig.  75,  VII),   which  lies  between 
the  tympanic  bulla,  the  paroccipital  process,  and  the  mastoid 
portion  of  the  periotic. 

g.  The  eighth  or  auditory  nerve  on  leaving  the  cranial 
cavity,  passes  with  the  facial  straight  into  the  auditory  capsule 
through  the  internal  auditory  meatus  (fig.  72,  20).     It  is 
then  distributed  to  the  organ  of  hearing. 

h.     The  ninth,  tenth  and  eleventh  nerves  leave  the  skull 


THE   SKELETON   OF   THE   DOG.      THE   SKULL.  401 

through  the  foramen  lacemm  posterms  (fig.  75,  IX,  X, 
XI),  a  large  space  lying  between  the  auditory  bones  and  the 
exoccipital. 

i.  Finally,  the  twelfth  nerve,  the  hypoglossal,  passes  out 
through  the  prominent  condylar  foramen  (fig.  75,  XII), 
which  perforates  the  exoccipital  just  behind  the  foramen 
lacerum  posterius. 

II.     OTHER  OPENINGS  IN  THE  SKULL. 

a.  The  anterior  narial  opening  lies  at  the  anterior  end 
of  the  skull,  and  is  bounded  by  the  premaxillae  and  nasals. 
In  the  natural  condition  it  is  divided  into  two  by  a  vertical 
partition,    formed   by  the  narial  septum,   the  anterior  un- 
ossified  j5art  of  the  mesethmoid. 

b.  Penetrating  the  middle  of  the  maxilla  at  the  side  of 
the  face  is  the  rather  large  infra-orbital  foramen  (fig.  73,  11), 
through  which  part  of   the  second  branch  of  the  trigeminal 
nerve  passes  out  from  the  orbit  to  the  side  of  the  face. 

c.  Several  foramina  are  seen  perforating  the  anterior  part 
of  the  orbit.     The  most  dorsal  of  these,  perforating  the  lach- 
rymal bone,  is  the  lachrymal  foramen  (fig.  73,  13).     Lying 
below  and  slightly  external  to  this  is  a  large  foramen,  through 
which  part  of  the  second  branch  of  the  trigeminal  enters  on 
its  way  to  the  infra-orbital  foramen  and  so  to  the  side  of  the 
face.     Lastly,  lying  below  these,  and  perforating  the  palatine, 
are    two    closely    apposed    foramina,    the    internal    orbital 
foramina,   through   which    part   of  the  first  or   ophthalmic 
branch  of  the  trigeminal  nerve  leaves  the  orbit,  passing  into 
the  nasal  cavity. 

d.  The  anterior  part  of  the  palate  between  the  premaxillae 
and  the  maxillae  is  perforated  by  a  pair  of  long  closely  apposed 
apertures,   the   anterior   palatine   foramina   (fig.  75,   19). 
They  transmit  part  of  the  trigeminal  nerve. 

e.  Towards  the  posterior  part  of  the  palate  are  two  pairs 
of  small  posterior  palatine  foramina  (fig.  75,  18).     These 

R.  26 

f 


402          THE  VERTEBRATE  SKELETON. 

perforate  the  palatine  and  transmit  branches  of  the  trigeminal 
nerve  and  certain  blood-vessels. 

f.  The  posterior  narial  opening  is  bounded  chiefly  by 
the  palatines. 

g.  The  alisphenoid  canal  (fig.  75,  21)  is  a  short  canal 
penetrating  the  base  of  the  alisphenoid  bone,  and  transmitting 
the  external   carotid   artery.     It   lies    between  the  foramen 
rotundum  and  the  foramen  ovale. 

h.  Between  the  auditory  bulla  and  the  foramen  ovale  are 
seen  two  openings.  The  more  external  of  these  is  the  opening 
of  the  Eustachian  canal  (fig.  75,  22),  which  communicates 
with  the  tympanic  cavity.  The  more  internal  is  the  foramen 
lacerum*  medium  (fig.  75,  9),  through  which  the  internal 
carotid  enters  the  cranial  cavity. 

i.  The  external  auditory  aperture  (fig.  75,  7)  is  a  large 
opening  with  rough  edges  at  the  outer  side  of  the  tympanic  bulla. 

j.  Between  it  and  the  glenoid  surface  of  the  squamosal  is 
the  postglenoid  foramen  (fig.  75,  10)  through  which  a  vein 
passes  out. 

k.  Lastly,  there  is  the  great  foramen  magnum  (fig.  75,  2), 
between  the  occipital  condyles.  Through  it  the  brain  and 
spinal  cord  communicate. 

C.     THE  RIBS  AND  STERNUM. 

These,  together  with  the  thoracic  vertebrae,  form  the 
skeletal  framework  of  the  thorax.  Each  rib  is  a  curved  rod, 
which  at  its  dorsal  end  is  movably  articulated  to  the  vertebra, 
and  at  its  ventral  end  is  either  connected  with  the  sternum,  or 
ends  freely.  In  the  dog  there  are  thirteen  pairs  of  ribs,  nine 
pairs  of  which  are  directly  connected  with  the  sternum,  while 
the  remaining  four  end  freely  and  are  known  as  floating  ribs. 
Each  rib  is  obviously  divided  into  two  parts,  a  dorsal  or  ver- 
tebral part,  and  a  ventral  or  sternal  part.  The  vertebral 
portion,  which  forms  about  two-thirds  of  the  whole  rib,  is  a 
flattened,  regularly  curved  rod,  completely  ossified.  Its  dorsal 


THE   SKELETON    OF   THE    DOG.      THE    RIBS. 


403 


end  is  rounded,  forming  the  head  or  capitlllum,  which 
articulates  with  a  concave  surface  furnished  partly  by  the  cor- 
responding vertebra  and  partly  by  the  vertebra  next  in  front. 
The  last  three  or  four  however  articulate  with  one  vertebra 
only.  A  short  way  behind  the  capitulum  on  the  dorsal  side  of 
the  rib  is  a  rounded  outgrowth,  the  tubercle  or  tuberculum, 
by  means  of  which  the  rib  articulates  with  the  transverse 
process.  The  portion  of  the  rib  between  the  head  and  the 
tubercle  is  known  as  the  neck.  The  sternal  portion  of  the 
rib  (fig.  76)  is  a  short  bar  of  calcined  or  imperfectly  ossified 
cartilage,  about  one-third  of  the  length  of  the  corresponding 
bony  portion.  The  anterior  sternal  ribs  are  somewhat  more 
cartilaginous  than  the  posterior  ones.  The  vertebral  portions 


FIG.  76.     STERNUM  AND  STERNAL  RIBS  OF  A  DOG  (Canis  familiaris) 


1.  presternum.  4. 

2.  first    sternebra    of  mesoster- 

num. 

3.  last    sternebra    of    mesoster- 

num.  o. 


xiphisternum.  The  flattened 
cartilaginous  plate  termi- 
nating the  xiphisternum  is 
not  shown. 

first  sternal  rib. 

26—2 


404  THE  VERTEBRATE  SKELETON. 

increase  in  length  from  the  first  which  is  very  stout,  and  has 
the  capitulum  and  tuberculum  very  distinct,  to  about  the 
eighth  or  ninth  ;  afterwards  they  gradually  diminish  in  size. 
The  first  nine  to  eleven  have  the  capitula  and  tubercula  sepa- 
rate, afterwards  they  gradually  merge  together. 

THE  STERNUM. 

This  is  an  elongated  cylindrical  structure  lying  in  the  mid- 
ventral  wall  of  the  thorax,  and  is  divided  into  eight  segments 
or  sternebrae.  The  anterior  segment,  the  presternum 
(fig.  76,  1)  or  manubrium  sterni  is  expanded  in  front;  the 
next  six  segments,  which,  together  form  the  mesosternum 
are  elongated,  somewhat  contracted  in  the  middle  and  ex- 
panded at  the  ends.  The  last  segment  or  xiphisternum 
(tig.  76,  4)  is  long  and  narrow,  and  terminates  in  a  flattened 
expanded  plate  of  cartilage.  The  first  pair  of  sternal  ribs 
articulate  with  the  sides  of  the  presternum,  and  the  remaining 
pairs  between  the  successive  sternebrae.  Between  the  last 
sternebra  and  the  xiphisternum  two  pairs  articulate.  De- 
velopment shows  that  the  sternum  is  formed  by  the  union 
in  the  middle  line  of  two  lateral  portions  ;  this  can  be  well 
seen  in  the  presternum  and  xiphisternum  of  the  puppy,  but  no 
traces  of  this  median  division  remain  in  the  adult  dog. 

2.     THE  APPENDICULAR  SKELETON. 

The  appendicular  skeleton  consists  of  the  bones  of  the 
anterior  and  posterior  limbs,  and  of  their  respective  supports, 
the  pectoral  and  pelvic  girdles. 

THE  PECTORAL  GIRDLE. 

The  pectoral  girdle  lies  external  to  the  ribs,  and  has  no 
bony  attachment  to  the  axial  skeleton.  In  almost  all 
Mammalia  it  is,  as  compared  with  that  in  Sauropsids,  very 
incomplete ;  and  in  the  dog  it  is  even  more  reduced  than  in 
the  majority  of  Mammalia.  The  dorsal  portion  or  scapula  is 
well  developed,  but  the  ventral  portion  is  almost  entirely  absent. 

The  scapula  is  somewhat  triangular  in  shape,  the  apex 


THE  SKELETON  OF  THE  DOG.   PECTORAL  GIRDLE.  405 

being  directed  downwards  and  forwards,  and  being  expanded 
to  form  the  shallow  glenoid  cavity  with  which  the  head  of 
the  humerus  articulates.  The  inner  surface  of  the  scapula  is 
nearly  flat,  while  the  outer  is  drawn  out  into  a  very  prominent 
ridge,  the  spine,  which,  arising  gradually  near  the  dorsal  end, 
runs  downwards,  dividing  the  surface  into  two  nearly  equal 
parts,  the  prescapular  and  postscapular  fossae,  and  ends 
in  a  short  blunt  process,  the  acromion.  The  anterior  border 
of  the  scapula  is  somewhat  curved,  and  is  called  the  coracoid 
border ;  it  is  terminated  ventrally  by  a  slight  blunt  swelling, 
the  coracoid  process,  which  ossifies  from  a  different  centre 
from  the  rest  of  the  scapula,  and  is  probably  the  sole  repre- 
sentative of  the  coracoid.  The  dorsal  or  suprascapular 
border  of  the  scapula  is  rounded,  while  the  posterior  or 
glenoid  border  is  nearly  straight.  The  clavicle1  or  collar 
bone,  which  in  a  large  proportion  of  mammals  is  well  seen,  in 
the  dog  is  very  imperfectly  developed ;  it  is  short  and  broad, 
and  is  suspended  in  the  muscles,  not  reaching  either  the 
scapula  or  sternum. 

THE  ANTERIOR  LIMB. 

The  anterior  limb  of  the  dog  is  divisible  into  the  usual 
three  portions,  the  brachium  or  upper  arm,  the  anti- 
brachium  or  fore-arm,  and  the  manus  or  wrist  and  hand. 

The  brachium  or  upper  arm  includes  only  a  single  bone, 
the  humerus. 

The  humerus  is  a  stout  elongated  bone,  articulating  by 
its  large  proximal  head  (fig.  77,  1)  with  the  glenoid  cavity  of 
the  scapula,  and  at  its  distal  end  by  the  trochlea  with  the 
bones  of  the  fore- arm.  The  head  passes  on  its  inner  side  into 
an  area  roughened  for  the  attachment  of,  muscles  and  called 
the  lesser  tuberosity  (fig.  77,  2) ;  while  in  front  it  is  divided 
by  the  shallow  bicipital  groove  from  a  large  roughened  area, 
the  greater  tuberosity  (fig.  77,  3),  which  is  continued  as  a 

1  See  note  to  p.  25. 


406  THE  VERTEBRATE  SKELETON. 

slight  roughened  ridge,  extending  about  one-third  of  the  way 
down  the  outer  side  of  the  shaft.  This  ridge,  which  in  many 
animals  is  much  more  strongly  developed  than  it  is  in  the  dog, 
is  called  the  deltoid  ridge.  The  trochlea  (fig.  77,  5)  at  the 
distal  end  of  the  bone  is  a  pulley-like  surface,  elevated  at 
the  sides  and  grooved  in  the  middle.  It  articulates  with  the 
radius  and  ulna  of  the  fore-arm.  On  each  side  of  it  are  slight 
roughened,  projections,  the  internal  and  external  condyles 
(fig.  77,  7).  In  the  cat  and  many  other  animals  there  is  a 
foramen,  the  ent-epicondylar  foramen  above  the  internal 
condyle,  but  in  the  dog  this  is  not  developed.  Passing  up 
the  shaft  from  the  external  condyle  is  a  slight  ridge,  the  supi- 
nator  or  ectocondylar  ridge  ;  this  is  better  developed  in 
many  mammals.  Immediately  above  the  trochlea  in  front 
and  behind  are  the  deep  supra-trochlear  fossae,  which 
communicate  with  one  another  through  the  supra-trochlear 
foramen  (fig.  77,  8).  The  posterior  of  these,  the  olecranon 
fossa,  is  much  the  deeper,  and  receives  the  olecranon  process 
of  the  ulna  when  the  arm  is  extended.  The  head  and 
tuberosities  of  the  humerus  ossify  from  one  centre,  the  shaft 
from  a  second,  and  the  trochlea  and  condyles  from  a  third. 

The  fore-arm  or  antibrachium  contains  two  bones, 
the  radius  and  ulna ;  they  are  immovably  articulated  with 
one  another,  but  not  fused.  The  pre-axial  bone,  the  radius 
(fig.  77,  B),  which  lies  more  or  less  in  front  of  the  ulna,  is 
external  to  the  ulna  at  its  proximal  end,  and  at  its  distal  end  is 
internal  to  that  bone.  It  articulates  with  the  external  portion 
of  the  trochlea,  while  the  ulna  articulates  with  the  internal 
portion.  It  is  a  straight  bone  with  its  distal  end  slightly  larger 
than  its  proximal  end.  The  proximal  end  articulates  with  the 
trochlea,  the  distal  ehd  with  the  bones  of  the  carpus. 

The  post-axial  bone,  the  ulna  (fig.  77,  C),  has  the  proximal 
end  much  enlarged,  forming  the  olecranon  (fig.  77,  11),  and 
tapers  gradually  to  the  distal  end.  Near  its  proximal  end 
the  ulna  is  marked  by  a  deep  sigmoid  notch,  which  bears 


THE   SKELETON   OF   THE   DOG.      ANTERIOR   LIMB.      407 

on  its  inner  side  a  concave  surface  (fig.  77,  12)  for  articulation 
with  the  trochlea.     The  pointed  proximal  end  of  the  sigmoid 


FIG.  77.    BONES  OF  THE  LEFT  UPPER  ABM  AND  FOKE-ABM  OF  A  DOG 

{ Cam's  familiaris)  x  \. 

A,  humerus  (seen  from  the  posterior  side) ;  B,  radius,  C,  ulna,  both  seen 
from  the  anterior  side. 

1.  head.  9.    proximal  end  of  the  radius. 

2.  lesser  tuberosityJP  4W-         '    10. 

3.  greater  tuberosity.  11. 

4.  shaft  of  the  humerus.  12. 

5.  trochlea. 

6.  internal  condyle.  13. 

7.  external  condyle. 


8.     supra-trochlear  foramen. 


14. 


shaft  of  the  radius. 

olecranon. 

surface  for  articulation  with 

the  trochlea. 
surface  for  articulation  with 

the  radius, 
distal  end  of  the  ulna. 


408  THE  VERTEBRATE  SKELETON. 

notch  is  called  the  coronoid  process.  Somewhat  in  front 
of  and  below  the  sigmoid  notch  is  a  smaller  hollow  (fig.  77,  13), 
with  which  the  radius  articulates. 

In  the  young  animal  the  ends  of  both  radius  and  ulna  are 
seen  to  ossify  from  centres  different  from  those  forming  the 
shafts.  The  epiphyses  forming  both  ends  of  the  radius,  and  the 
distal  end  of  the  ulna  are  large,  while  that  at  the  proximal  end 
of  the  ulna  is  small,  and  forms  only  the  end  of  the  olecranon. 

The  Maims  is  divided  into 

a.  The  carpus  or  wrist,   formed   of   a  group  of   small 
bones. 

b.  The   hand,    which    includes    firstly    some    elongated 
bones,  the  metacarpals,   forming  what  corresponds  to  the 
palm  of  the  hand,  and  secondly  the  phalanges,  which  form  the 
fingers. 

The  Carpus  or  wrist.  The  carpus  of  the  dog  consists  of 
seven  small  bones,  arranged  in  a  proximal  row  of  three,  and 
a  distal  row  of  four.  It  differs  much  from  the  simpler  type 
met  with  in  the  newt.  The  largest  bone  of  the  proximal  row 
is  the  scapho-lunar  (fig.  80, 1),  formed  by  the  fused  scaphoid 
(radiale),  lunar  (intermedium),  and  centrale  ;  it  has  a  large 
convex  proximal  surface  for  articulation  with  the  radius,  and 
articulates  distally  with  the  trapezium,  trapezoid,  and  magnum, 
and  internally  with  the  cuneiform.  The  cuneiform  (ulnare) 
(fig.  80,  2)  has  a  posterior  rounded  surface  articulating  with 
the  ulna  ;  it  articulates  in  front  with  the  unciform,  arid  in- 
ternally with  the  pisiform  (fig.  80,  7),  which  is  a  compara- 
tively large  sesamoid  bone  on  the  ulnar  side  of  the  carpus. 
Frequently  also  there  is  a  small  sesamoid*  bone  on  the  radial 
side  of  the  carpus.  The  trapezium  (carpale  1),  trapezoid 
(carpale  2),  and  magnum  (carpale  3)  (fig.  80,  5)  are  all  small 
bones,  and  support  respectively  the  first,  second,  and  third 
metacarpals.  The  unciform  (carpalia  4  and  5)  (fig.  80,  6) 
is  larger,  and  supports  the  fourth  and  fifth  metacarpals. 


THE   SKELETON   OF   THE   DOG.      PELVIC   GIRDLE.       409 

The  hand  has  five  digits,  each  consisting  of  an  elongated 
metacarpal,  followed  by  phalanges,  the  last  of  which,  the 
ungual  phalanx,  is  pointed  and  curved,  and  bears  the  claw. 
Each  of  the  metacarpals  is  seen  in  the  young  animal  to  have 
its  distal  end  formed  by  a  prominent  epiphysis,  and  each  of 
the  phalanges,  except  those  bearing  the  claws,  has  a  similar 
epiphysis  at  its  proximal  end. 

The  pollex  (fig.  80,  A,  I)  is  far  shorter  than  the  other  digits, 
and  normally  does  not  touch  the  ground  in  walking.  It  has 
only  two  phalanges,  while  each  of  the  other  digits  has  three. 
A  pair  of  small  sesamoid  bones  are  developed  on  the  ventral  or 
fiexor  side  of  the  metacarpo-phalangeal  articulations  of  all  the 
digits  except  the  pollex.  Frequently  similar  sesamoid  bones 
occur  also  on  the  dorsal  side  of  the  phalangeal  articulations. 

THE  PELVIC  GIRDLE. 

The  pelvic  girdle  consists  of  two  halves,  which  lie  nearly 
parallel  to  the  vertebral  column. 

Each  half  is  firmly  united  to  its  fellow  in  a  ventral 
symphysis  behind,  and  is  in  front  expanded  and  united  to  the 
sacrum.  Each  half  or  innominate  bone  is  seen  in  the  young 
animal  to  consist  of  four  distinct  parts,  the  ilium  or  dorsal 
element,  the  pubis  or  anterior  ventral  element,  the  ischium 
or  posterior  ventral  element,  and  a  small  fourth  part,  the 
acetabular  or  cotyloid  bone,  wedged  in  between  the  three 
others.  These  parts,  though  all  distinct  in  the  young  animal, 
are  in  the  adult  so  completely  fused  that  their  respective 
boundaries  cannot  be  distinguished.  At  about  the  middle  of 
the  outer  surface  of  the  innominate  bone  is  a  very  deep  cavity, 
the  acetabulum  (fig.  78,  A,  1)  with  which  the  head  of  the 
femur  articulates ;  all  the  bones  except  the  pubis  take  part 
in  its  formation. 

The  ilium  is  a  rather  long  bone,  expanded  in  front  and 
contracted  behind ;  it  forms  about  half  the  acetabulum.  On 
its  inner  or  sacral  surface  (fig.  78,  4)  is  a  large  roughened 


410 


THE  VERTEBRATE  SKELETON. 


patch  for  articulation  with  the  sacrum  ;  its  outer  or  gluteal 
surface  is  concave.  The  posterior  part  of  the  bone  is  flattened 
below,  forming  the  narrow  iliac  surface  (fig.  78,  A,  5). 


10- 


FIG.  78.    EIGHT  INNOMINATE  BONE,  A,  or  A  FULL-GROWN  TERRIER,  B,  OF 

A  COLLIE  PUPPY,      x  1. 
A  is  seen  from  the  ventral  side,  B  from  the  inner  or  sacral  side. 


acetabulum.  8. 

thyroid  foramen.  9. 

supra-iliac  border  of  ilium.  10. 

sacral  surface.  11. 

iliac  surface.  12. 

acetabular  border.  13. 

pubic  border.  14. 


ischial  border. 

ischium. 

tuberosity  of  ischium. 

ischial  symphysis. 

pubis. 

pubic  symphysis. 

cotyloid  or  acetabular  bone. 


The  ischium  (fig.  78,  9)  is  a  wide  flattened  bone  forming 
the  posterior  part  of  the  innominate  bone.  It  meets  the 
pubis  ventrally,  but  is  separated  from  it  for  the  greater  part 
of  its  length  by  the  large  obturator  or  thyroid  foramen 
(fig.  78,  2).  At  its  posterior  end  externally  it  bears  a  rather 


THE   SKELETON   OF  THE   DOG.      PELVIC   GIRDLE.     411 

prominent  roughened  ischial  tuberosity  (fig.  78,  A,  10). 
The  ischium  meets  its  fellow  in  a  ventral  symphysis,  and 
forms  about  one-third  of  the  acetabulum. 


FIG.  79.    FRONT  VIEW  OF  THE  LEFT  LEG  BONES  OF  A  DOG  (Canis 

familiaris)  x  ^. 
A  femur,  B  tibia,  C  fibula,  D  patella. 

1.  head  of  femur.  5.     external  condyle. 

2.  neck.  6.     internal  condyle. 

3.  great  trochanter.  7.     fabella. 

4.  shaft.  8.     cnemial  crest. 

The  pubis  (fig.  78,  12)  is  smaller  than  either  the  ischium 
or  ilium  ;  it  does  not  take  part  in  the  formation  of  the  aceta- 
bulum, and  like  the  ischium,  meets  its  fellow  in  a  ventral 
symphysis.  The  acetabular  bone  (fig.  78,  B,  14)  is  small 


412          THE  VERTEBRATE  SKELETON. 

and  triangular,  and  is  wedged  in  between  the  other  three.     It 
forms  about  one-sixth  of  the  acetabulum. 


THE  POSTERIOR  LIMB. 

The  posterior  limb,  like  the  anterior,  is  divisible  into  three 
parts;  these  are  the  thigh,  the  crus  or  shin,  and  the  pes. 

The  thigh  contains  only  a  single  bone,  the  femur. 

The  femur  is  a  long  straight  bone  with  a  nearly  smooth 
shaft  and  expanded  ends.  The  proximal  end  bears  on  its 
inner  side  the  large  rounded  head  (fig.  79,  A,  1)  which 
articulates  with  the  acetabulum.  External  to  the  head  and 
divided  from  it  by  a  deep  pit  is  a  large  rough  outgrowth, 
the  great  trochanter  (fig.  79,  3).  The  deep  pit  is  the 
trochanteric  or  digital  fossa.  On  the  inner  side  below  the 
head  is  a  smaller  roughened  surface,  the  lesser  trochanter. 
The  lower  or  distal  end  of  the  bone  bears  two  prominent 
rounded  surfaces,  the  condyles,  which  articulate  with  the 
tibia.  They  are  separated  from  one  another  by  the  deep 
intercondylar  notch,  which  is  continued  above  and  in  front 
as  a  shallow  groove,  lodging  a  large  sesamoid  bone,  the  patella 
or  knee-cap.  At  the  back  of  the  knee-joint  are  a  pair  of 
smaller  sesamoids,  the  fabellae  (fig.  79,  7). 

In  the  young  animal  there  are  three  epiphyses  to  the  shaft 
of  the  femur,  one  forming  the  head,  one  the  great  trochanter, 
and  one  the  distal  end. 

The  crus  or  shin  contains  two  bones,  the  tibia  and 
fibula.  The  tibia  is  a  fairly  thick  straight  bone,  expanded 
at  both  ends,  especially  at  the  head  or  proximal  end.  The 
proximal  end  is  triangular  in  cross  section,  and  bears  two  facets 
for  articulation  with  the  condyles  of  the  femur.  The  anterior 
surface  of  the  proximal  end  of  the  tibia  is  marked  by  the 
strong  cnemial  crest  (fig.  79,  8),  which  runs  some  way  down 
the  shaft.  The  distal  end  of  the  tibia  articulates  with  the 
astragalus  by  an  irregular,  somewhat  square  surface. 


THE   SKELETON   OF   THE   DOG.      POSTERIOR   LIMB.      413 

The  shaft  of  the  tibia  ossifies  from  one  centre,  the  distal  end 
from  a  second,  and  the  proximal  end  from  two  more. 

The  fibula  (tig.  79,  C)  is  a  distinct  but  very  slender  bone, 
somewhat  expanded  at  both  ends.  It  lies  external  to  the 


FIG.  80.     A,  BIGHT  MANUS,  B,  RIGHT  PBS  OF  A  DOG  (Cams  fami 
liaris)x%  (after  VON  ZITTEL). 

1.  bone  representing  the   fused 

scaphoid,    lunar    and  cen- 
trale. 

2.  cuneiform. 

3.  trapezium. 

4.  trapezoid. 

5.  magnum. 

6.  unciform. 

7.  pisiform. 


9.     fifth  metacarpal. 
10.     astragalus, 
calcaneum. 
navicular. 
middle  cuneiform, 
external  cuneiform, 
cuboid, 
first  metatarsal. 


11. 

12. 
13. 
14. 
15. 
16. 


8.     first  metacarpal. 


The  digits  are   numbered  with 
Eoman  numerals. 


414          THE  VERTEBRATE  SKELETON. 

tibia  and  articulates  by  its  proximal  end  with  the  head  of  the 
tibia,  and  by  its  distal  end  with  the  calcaneum.  Its  shaft 
and  proximal  end  ossify  from  one  centre,  and  its  distal  end 
from  a  second. 


The  Pes. 

The  structure  of  the  pes  corresponds  closely  with  that  of 
the  manus.  It  is  divided  into  : — 

a.  The  tarsus  or  ankle  formed  of  a  group  of  small 
bones. 

6.  The  foot,  which  includes,  firstly,  some  elongated  bones, 
the  metatarsals,  forming  what  corresponds  to  the  sole  of 
the  foot,  and  secondly  the  phalanges,  which  form  the  toes. 

The  Tarsus.  The  tarsus  of  the  dog  consists  of  seven  bones 
arranged  in  two  rows,  of  two  and  four  respectively,  with  a 
centrale  between  them.  The  two  bones  of  the  proximal  row 
are  the  astragalus  and  calcaneum. 

The  astragalus  (fig.  80,  10)  corresponds  to  the  fused 
tibiale  and  intermedium  of  the  typical  tarsus.  Its  proximal 
end  is  much  wider  than  its  distal  end,  and  forms  a  large 
rounded  condyle  articulating  with  the  tibia,  while  its  pos- 
terior end  meets  the  navicular.  It  lies  to  the  dorsal  side  of 
the  foot. 

The  calcaneum  (fibulare)  (fig.  80,  11),  the  thickest  bone 
in  the  pes,  lies  somewhat  behind,  and  to  the  outer  side  of  the 
astragalus.  It  articulates  with  the  astragalus  and  fibula,  and 
is  drawn  out  behind  into  a  long  rounded  process,  which  forms 
the  heel,  and  is  in  the  young  animal  terminated  by  an  epi- 
physis.  Between  the  proximal  and  distal  rows  of  tarsals  is 
the  navicular  (centrale)  (fig.  80,  12),  a  somewhat  flattened 
and  square  bone  articulating  with  the  astragalus. 

The  distal  row  of  tarsals  consists  of  four  bones.  The 
internal  cuneiform  (tarsale  1)  is  a  smooth  flattened  bone 
lying  to  the  inner  side  of  the  foot;  it  articulates  with  the 


THE   SKELETON   OF   THE    DOG.      THE    PES.  415 

first  metatarsal  and  with  the  navicular.  The  middle  cunei- 
form (tarsale  2)  (fig.  80,  13)  is  a  still  smaller  bone,  lying 
external  to  the  internal  cuneiform.  It  articulates  with  the 
second  metatarsal  and  with  the  navicular.  The  external 
cuneiform,  (tarsale  3)  (fig.  80,  14)  is  a  larger,  somewhat  square 
bone  lying  external  to  the  middle  cuneiform.  It  articulates 
with  the  third  metatarsal  and  with  the  navicular.  The  cuboid 
(tarsalia  4  and  5)  (fig.  80,  15)  is  a  considerably  larger  bone 
lying  to  the  outer  side  of  the  foot.  It  articulates  with  the 
fourth  and  fifth  metatarsals  and  with  the  calcaneum. 

The  pes  has  sometimes  five  digits,  sometimes  four,  the 
hallux  being  absent.  Even  when  present  the  hallux  (fig.  80, 
B,  I)  is  commonly  much  reduced,  and  may  be  quite  vestigial, 
and  represented  only  by  a  small  nodular  metatarsal. 

Each  of  the  other  digits  consists  of  a  long  metatarsal, 
which  in  the  young  animal  has  a  prominent  epiphysis  at  its 
distal  end,  and  of  three  phalanges.  The  proximal  and  middle 
phalanges  have  epiphyses  at  their  proximal  ends,  while  the 
distal  phalanx  is  without  epiphyses  and  is  claw-shaped. 


CHAPTER   XXII. 

GENERAL    ACCOUNT   OF   THE   SKELETON   IN 
MAMMALIA. 

THE    EXOSKELETON   AND   VERTEBEAL   COLUMN. 

EPIDERMAL  EXOSKELETON. 

Hair,  which  forms  the  characteristic  Mammalian  exo- 
skeleton  varies  much  in  different  animals,  and  in  different 
parts  of  the  same  animal.  A  large  proportion  of  mammals 
have  the  surface  fairly  uniformly  covered  with  hair  of  one 
kind  only.  In  some  forms  however  there  are  two  kinds  of 
hair,  a  longer  and  stiffer  kind  alone  appearing  on  the  surface, 
and  a  shorter  and  softer  kind  forming  the  under  fur.  In 
most  mammals  hairs  of  a  special  character  occur  in  certain 
regions,  such  as  above  the  eyes,  on  the  margins  of  the 
eyelids,  and  on  the  lips  and  cheeks,  here  forming  the  vibrissae 
or  whiskers. 

Sometimes  as  in  Hippopotamus,  Orycteropus  and  the  Sirenia, 
the  hair,  though  scattered  over  the  whole  surface,  is  extremely 
scanty,  while  in  the  Cetacea  it  is  limited  to  a  few  bristles 
in  the  neighbourhood  of  the  mouth,  or  may  even  be  absent 
altogether  in  the  adult.  In  most  mammals  the  hairs  are 
shed  and  renewed  at  intervals,  sometimes  twice  a  year,  before 
and  after  the  winter.  The  vibrissae  or  large  hairs  which 
occur  in  many  animals  upon  the  upper  lip,  and  the  mane  and 
tail  of  Equidae  are  probably  persistent. 


THE   SKELETON   IN   MAMMALIA.      EXOSKELETON.       417 

In  the  hedgehogs,  porcupines  and  Echidna  certain  of  the 
hairs  are  modified  and  greatly  enlarged,  forming  stiff  spines. 
Similar  spines  occur  in  the  young  of  Centetes,  and  in  Acan- 
thornys  among  the  Muridae. 

Several  other  forms  of  epidermal  exoskeleton  are  met  with 
in  mammals,  including  : — 

(a)  Scales.     These  overlie  the  bony  scutes  of  armadillos 
and  occur  covering  the  tail  in  several  groups  of  mammals,  such 
as  beavers  and  rats.     In  the  Manidae  the  body  is  covered  by 
flat  scales  which  overlap. 

(b)  The  horns  of  Bovine  Ruminants.     These,  which  must 
on  no  account  be  confused  with  antlers,  are  hollow  cases  of 
hardened  epidermis  fitting  on  to  bony  outgrowths  of  the  frontals. 
In  almost  every  case  they  are  unbranched  structures  growing 
continuously  throughout  life,  and  are  very  rarely  shed  entire. 
In  the  Prongbuck  A  ntilocapra  however  they  are  bifurcated  and 
are  periodically  shed.      Horns  are  nearly  always  limited  to  a 
single  pair,  but  the  four-horned  antelope  Tetraceros  has  two 
pairs,  the  anterior  pair  being  the  smaller. 

(c)  The  horns  of  Rhinoceroses.      These   are   conical 
structures   composed   of  a  solid   mass  of  hardened  epidermal 
cells  growing  from  a  cluster  of  long  dermal  papillae.     From 
each  papilla  there  grows  a  fibre  which  resembles  a  thick  hair, 
and  cementing  the  whole  together  are  cells  which  grow  from 
the  interspaces  between  the  papillae.     These  fibres  differ  from 
true    hairs    in    not    being  developed   in    pits  in  the  dermis. 
Rhinoceros  horns  may  be  either  one  or  two  in  number,  and 
are  borne  on  the  fronto-nasal  region  of  the  skull.     They  vary 
much  in  length,   the  longest  recorded   having  the  enormous 
length  of  fifty-seven  inches. 

(d)  Nails,  hoofs  and  claws.     In  almost  all   mammals 
except  the  Cetacea,  these  are  found  terminating  the  digits  of 
both    limbs.     Nails    are    more    or    less   flattened    structures, 
claws  are  pointed  and  somewhat  curved.     In  most  mammals 

R.  27 


418          THE  VERTEBRATE  SKELETON. 

the  nails  tend  to  surround  the  ends  of  the  digits  much  more 
than  they  do  in  man.  Sometimes  the  nail  of  one  digit  differs 
from  that  of  all  the  others ;  thus  the  second  digit  of  the  pes  in 
the  Hyracoidea  and  Lemuroidea  is  terminated  by  a  long  claw, 
the  other  digits  having  flat  nails.  In  the  Felidae  the  claws 
are  retractile,  the  ungual  phalanx  with  claw  attached  folding 
back  when  the  animal  is  at  rest  into  a  sheath,  above,  or  by 
the  side  of  the  middle  phalanx.  In  the  Sloths  and  Bats 
enormously  developed  claws  occur,  forming  hooks  by  which  the 
animals  suspend  themselves.  In  Notoryctes  the  third  and 
fourth  digits  of  the  manus  bear  claws  of  great  size;  simi- 
lar claws  occur  in  Chrysochloris,  being  correlated  in  each  case 
with  fossorial  habits.  The  nail  at  its  maximum  development 
entirely  surrounds  the  terminal  phalanx  of  the  digit  to  which 
it  is  attached,  and  is  then  called  a  hoof.  Hoofs  are  specially 
characteristic  of  the  Ungulata. 

(e)  Spurs  and  beaks  are  structures  which  are  hardly  re- 
presented among  mammals,  while  so  characteristic  of  birds. 
They  are  however  both  found  in  the  Monotremata.  In 
both  Echidna  and  Ornithorhynchus  the  male  has  a  peculiar 
hollow  horny  spur  borne  on  a  sesamoid  bone  articulated  to 
the  tibia.  The  jaws  in  Ornithorhynchus  are  cased  in  horny 
beaks  similar  to  those  of  birds,  and  are  provided  with  horny 
pads  which  act  as  teeth. 

(/)  Horny  plates  of  a  ridged  or  roughened  character 
occur  upon  the  anterior  portion  of  the  palate,  and  of  the  man- 
dibular  symphysis  in  all  three  genera  of  recent  Siren ia ;  also 
upon  the  toothless  anterior  portion  of  the  palate  in  Ruminants. 

(g)  The  baleen  of  whales  also  belongs  to  the  epidermal 
exoskeleton.  It  consists  of  a  number  of  flattened  horny  plates 
arranged  in  a  double  series  along  the  palate.  The  plates  are 
somewhat  triangular  in  form  and  have  their  bases  attached 
to  the  palate  at  right  angles  to  its  long  axis,  while  their  apices 
hang  downwards  into  the  mouth  cavity.  The  outer  edge 
of  each  plate  is  hard  arid  smooth,  while  the  inner  edge  and. 


THE     SKELETON    TN   MAMMALIA.      EXOSKELETON. 

apex  fray  out  into  long  fibres  which  look  like  hair.  At  the 
inner  edge  of  each  principal  plate  are  subsidiary  smaller  plates. 
The  plates  are  formed  of  a  number  of  fibres  each  developed 
round  a  dermal  papilla  in  the  same  way  as  are  the  fibres 
forming  the  horns  of  Rhinoceros.  Baleen  and  Rhinoceros 
horn  likewise  agree  in  that  the  fibres  are  bound  together  by 
less  hardened  epithelial  cells,  which  readily  wear  away  and 
allow  the  harder  fibres  to  fray  out.  The  greatest  develop- 
ment of  baleen  occurs  in  the  Northern  Right  whale,  Balaena 
mysticetus,  in  which  the  plates  number  three  hundred  and 
eighty  or  more  on  each  side,  and  reach  a  length  of  ten  or 
twelve  feet  near  the  middle  of  the  series. 

DERMAL  EXOSKELETON. 

Mammals  show  two  principal  kinds  of  exoskeletal  struc- 
tures which  are  entirely  or  partially  dermal  in  origin,  viz.  the 
bony  scutes  of  armadillos,  and  teeth. 

The  bony  scutes  of  armadillos  are  quadrate  or  polygonal 
in  shape  and  are  in  general  aggregated  together,  forming 
several  shields  protecting  various  re'gions  of  the  body.  The 
head  is  generally  protected  by  a  cephalic  shield,  the  anterior 
part  of  the  body  by  a  scapular,  and  the  posterior  by  a  pelvic 
shield.  The  tail  is  also  generally  encased  in  bony  rings,  and 
scutes  are  irregularly  scattered  over  the  surface  of  the  limbs. 
The  mid-body  region  is  protected  by  a  varying  number  of 
bands  of  scutes  united  by  soft  skin,  so  as  to  allow  of  move- 
ment. Corresponding  to  each  dermal  scute  is  an  epidermal 
plate.  In  Chlamydophorus  the  scutes  are  mainly  confined  to 
the  posterior  region  where  they  form  a  strong  vertically-placed 
shield  which  coalesces  with  the  pelvis.  The  anterior  part  of 
the  body  is  mainly  covered  by  horny  epidermal  plates  with 
very  little  ossification  beneath.  In  the  gigantic  extinct 
Glyptodonts  the  body  is  covered  with  a  solid  carapace 
formed  by  the  union  of  an  immense  number  of  plates,  and 
there  are  no  movable  rings.  The  top  of  the  head  is  defended 

27—2 


420          THE  VERTEBRATE  SKELETON. 

by  a  similar  plate,  the  tail  is  generally  encased  in  an  unjointed 
bony  tube,  and  there  is  commonly  a  ventral  plastron. 

In  Phocaena  phocaenoides  the  occurrence  of  vestigial  dermal 
ossicles  has  been  described,  and  in  Zeuglodon  the  back  was 
probably  protected  by  dermal  plates. 

TEETH1. 

Teeth  are  well  developed  in  the  vast  majority  of  mammalia, 
and  are  of  the  greatest  morphological  and  systematic  import- 
ance, many  extinct  forms  being  known  only  by  their  teeth. 
Mammalian  teeth  differ  from  those  of  lower  animals  in  various 
well-marked  respects.  (1)  They  are  attached  only  to  the 
maxillae,  premaxillae  and  mandible,  never  to  the  palatines, 
pterygoids  or  other  bones.  (2)  They  frequently  have  more 
than  one  root.  (3)  They  are  always,  except  in  some  Odon- 
toceti,  placed  in  distinct  sockets.  (4)  They  are  hardly  ever 
ankylosed  to  the  bone.  (5)  They  are  in  most  cases  markedly 
heterodont.  (6)  They  are  commonly  developed  in  two  sets, 
the  milk  dentition  and  permanent  dentition. 

It  sometimes  happens  that  teeth  after  being  formed  are 
reabsorbed  without  ever  cutting  the  gum.  This  is  the  case, 
for  instance,  with  the  upper  incisors  of  Ruminants. 

The  form  of  mammalian  teeth  varies  much,  some  are  simple 
conical  structures  comparable  to  those  of  most  reptiles,  and 
these  may  either  have  persistent  pulps,  as  in  the  case  of  the 
upper  canines  of  the  Walrus  and  the  tusks  of  Elephants,  or 
may  be  rooted  as  in  most  canine  teeth.  Some  teeth  have  chisel- 
shaped  edges,  and  this  may  be  their  original  form,  as  in  the 

1  See  W.  H.  Flower,  "Remarks  on  the  homologies  and  notation  of  the 
teeth  in  Mammalia,"  J.  Anat.  and  Physiol.  norm,  path.,  Vol.  iii.,  p.  262; 
R.  Owen,  Odontography,  London,  1840 — 45;  C.  S.  Tomes,  Manual  of 
Dental  Anatomy,  London,  1876.  See  also  H.  F.  Osborn,  "Recent  re- 
searches on  succession  of  teeth  in  Mammals,"  Amer.  Natural.,  xxvu., 
p.  493,  and  "Rise  of  Mammalia  in  N.  America,"  Stud.  Biol.  Lab.  Columb. 
Coll,  Zool.  i.,  no.  2. 


THE   SKELETON    IN    MAMMALIA.      THE   TEETH. 


421 


human  incisors,  or  may,  as  in  those  of  Rodents,  be  brought 
about  by  the  more  rapid  wearing  away  of  the  posterior  edge, 
the  anterior  edge  being  hardened  by  a  layer  of  enamel. 


m.c 


m2 


pnr»4 


FIG.  81.     SKULL  OF  A  YOUNG  INDIAN  EHINOCEBOS  (R.  unicornis), 

SHOWING  THE  CHANGE  OF  THE  -  DENTITION  X  \.   (Brit.  MllS.) 


1.  nasal. 

2.  frontal.      , 

3.  parietal. 

4.  zygomatic    process    of   squa- 

mosal. 

5.  jugal. 

wiJT      milk  incisor. 


inc.     milk  canine. 

mpmr     milk  premolar. 

Ir     first  incisor. 

c.     canine. 

pm2,  pms,  pm^.      2nd,   3rd   and 

4th  premolars. 
?«!,  w2.     first  and  second  molars. 


Then,  again,  the  crown  may,  as  in  the  majority  of  grinding 
teeth,  be'  more  or  less  flattened.  The  various  terms  used  in 
describing  some  of  the  forms  of  the  surface  of  grinding  teeth 
are  denned  on  page  345. 

The  teeth  of  the  Aard  Varks  are  compound,  and  differ 
completely  from  those  of  all  other  mammals  (see  p.  425). 

As  a  rule,  the  higher  the  general  organisation  of  an  anima] 


422  THE  VERTEBRATE  SKELETON. 

the  better  are  its  milk  teeth  developed,  and  the  more  do  they 
form  a  reproduction  on  a  small  scale  of  the  permanent  set. 
This  fact  is  well  seen  in  the  Primates,  Carnivora  and  Ungu- 
lata.  The  method  of  notation  by  which  the  dentition  of  any 
mammal  can  be  briefly  expressed  as  a  formula  has  been  already 
described.  The  regular  mammalian  arrangement  of  teeth  for 
each  side  is  expressed  by  the  formula 

i  -  c  -  pm  -  m  —  x  2  ;  total,  44. 
o       1  4        o 

MONOTEEMATA.  Iii  Echidna  teeth  are  quite  absent.  In 
the  young  Ornithorhynchus1  functional  molar  teeth  of  a  multi- 
tubercular  type  resembling  those  of  some  Mesozoic  mammalia 
are  present,  but  in  the  adult  they  disappear,  their  office  being 
discharged  by  horny  plates. 

MARSUPiALiA2  have  a  heterodont  dentition,  which  has 
generally  been  regarded  as  almost  monophyodont,  the  only 
tooth  which  has  an  obvious  deciduous  predecessor  being  the 
last  premolar.  The  researches  of  Rose3  and  Kiikenthal4  tend 
to  show  that  the  teeth  of  Marsupials  are  developed  in  the 
same  way  as  in  other  mammals,  and  are  diphyodont.  In 
the  case  of  the  premolars,  teeth  which  are  homologous  with 
the  permanent  teeth  of  other  mammals  begin  to  develop  as 
lateral  outgrowths  from  the  milk  teeth,  but  afterwards  be- 
come absorbed,  so  that  the  teeth  which  actually  persist  belong 
to  the  milk  series.  The  last  premolar,  however,  does  as 
a  rule  develop  and  replace  its  milk  predecessor;  sometimes, 
however,  as  in  Didelphys,  it  takes  its  place  among  the  milk 
molars  without  replacing  one  of  them. 

1  See  E.  B.  Poulton,  P.  R.  S.,  Feb.  1888,  and  Quart.  J.  Micr.  Sci., 
Vol.  xxix.  1889;  also  Oldfield  Thomas,  P.  E.  S.,  XLVI.  (1889). 

2  W.   H.  Flower,  Phil.  Trans.,  vol.  156,  pp.  631 — 641,  1867  ;   also 
Oldfield  Thomas,  Phil.  Trans.,  pp.  443—462,  1887. 

3  C.  Rose,  Anat.  Anz.  vn.,  p.  639. 

4  W.  Kiikenthal,  Anat.  Anz.  vi.,  p.  364. 


THE   SKELETON    IN   MAMMALIA.      THE   TEETH.        423 

The  types  of  dentition  characteristic  of  the  different  groups 
of  placental  mammals  may  mostly  be  paralleled  among 
the  Marsupials.  Thus  among  the  polyprotodont  forms  the 
Didelphyidae  or  opossums,  and  some  of  the  Dasyuridae,  such 
as  Sarcophilus  and  Thylacinus,  have  a  typical  carnivorous 
dentition  with  small  incisors,  large  canines,  and  molars  with 
pointed  compressed  crowns.  The  dental  formula  of  Tkylacinus, 

41          34 
is  i  •—  c  T  pin  ^m  -,  total  46. 
o        1  o         4 

In  Myrmecobius  five  or  six  molar  teeth  occur  on  each  side, 
and  the  total  number  of  teeth  reaches  fifty-two  or  fifty-six. 
The  teeth  bear  rows  of  tubercles,  and  resemble  those  of  the 
Multituberculate  mesozoic  Mammals1,  more  than  do  those  of 
any  other  living  form.  Calcified  teeth  have  recently  been 
described2  in  Myrmecobius  earlier  than  the  functional  or  milk 
set.  This  would  relegate  the  milk  teeth  of  mammals  in  general 

to  a  second  series,  and  the  permanent  teeth  to  a  third.     In 

31-24 
Notary ctes  the  dental  formula3  is  given  as  i  ^  c  ^  pm  ^  m  ^  , 

total  40.  The  canines  are  small,  and  the  anterior  molars 
have  strongly  developed  cusps,  and  much  resemble  those  of 
Chrysochloris  (Insectivora). 

Among  the  diprotodont  types  the  Phascolomyidae,  or 
Wombats,  have  a  dentition  recalling  that  of  the  Rodents.  All 
the  teeth  grow  from  persistent  pulps,  and  the  incisors  have 
enamel  only  on  the  anterior  surface  as  in  Rodents.  The  dental 

formula  is  i  |  c  |j  pm  ^  m^ ,  total  24.      There  are  indications 

of  a  vestigial  second  pair  of  incisors. 

The    Macropodidae,    or    Kangaroos,    have   a   herbivorous 

O          /A          1  \  9  A 

dentition  with  the  formula  i  -  c  ^  Q  '  pm^m-^.  The  incisors 
are  sharp  and  cutting,  and  are  separated  by  a  long  diastema  or 

i  See  p.  348.         2  W.  Leche,  Morph.  Jahrb.  xx.,  pp.  113—142  (1893). 
3  E.  C.  Stirling,  P.  Z.S.  1891,  p.  327. 


424          THE  VERTEBRATE  SKELETON. 

gap  from  the  molars,  which  have  their  crowns  marked  by  ridges 
or  cusps.  There  are  indications  of  several  vestigial  incisors. 

Coenolestes,  a  remarkable  form  recently  described  from 
America,  belongs  to  the  diprotodont  section,  and  is  the  only 
living  member  of  the  section  known  outside  the  Australian 
region1.  An  exceptional  dentition  is  seen  in  the  case  of  the 
extinct  Thylacoleo,  in  which  the  functional  teeth  are  reduced 
to  two  pairs;  one  pair  of  large  cutting  incisors  and  one  of 
compressed  sharp-edged  premolars. 

EDENTATA.  Some  Edentata,  viz.  the  anteaters  (Myrme- 
cophagidae)  are,  as  far  as  is  known,  absolutely  toothless  at  all 
stages  of  their  existence  ;  being  the  only  mammals  except 
Echidna  in  which  no  tooth  germs  have  been  discovered ; 
others,  viz.  the  Manidae,  though  showing  foetal  tooth  germs, 
are  quite  toothless  in  post-foetal  life ;  others,  viz.  some  of 
the  armadillos,  have  the  largest  number  of  teeth  met  with  in 
land  mammals.  The  teeth  are  homodont  except  in  the  Aard 
Yarks,  and  grow  from  persistent  pulps.  In  the  sloths  (Brady- 
podidae)  and  the  Megatheriidae,  there  are  five  pairs  of  teeth  in 
the  upper  and  four  in  the  lower  jaw.  The  teeth  of  sloths  consist 
of  a  central  axis  of  vasodentine,  surrounded  firstly  by  a  thin  coat- 
ing of  hard  dentine,  and  secondly  by  a  thick  coating  of  cement. 

In  no  living  Edentate  have  the  teeth  any  enamel;  it  has, 
however,  been  described  as  occurring  in  certain  early  Mega- 
theroid  forms  from  S.  America2,  and  an  enamel  organ  has 
also  been  discovered  in  an  embryo  Dasypus*.  In  the  Arma- 
dillos (Dasypodidae)  the  number  of  teeth  varies  from  f  or  \  in 
Tatusia,  to  upwards  of  f  J-  in  Priodon,  which  therefore  may  have 
upwards  of  a  hundred  teeth,  the  largest  number  met  with  in  any 
land  mammal.  In  Tatusia  all  the  teeth  except  the  last  are 

1  0.  Thomas,  P.  Z.  S.,  1895,  p.  870. 

2  ¥.Ameghino,Bull.Ac.  Argen.xu.  p.  437.  According  to  H.  Burmeister, 
Annal.  Mus.  Buenos  Aires,  in.  401  (1891),  enamel  does  not  occur,  osteo- 
dentine  having  been  mistaken  for  it. 

3  E.  Ballowitz,  Arch.  Mikr.  Anat.  XL.  p.  133. 


THE   SKELETON    IN   MAMMALIA.      THE   TEETH.        425 

preceded  by  two-rooted  milk  teeth.  The  Aard  Varks  are 
diphyodont,  and  milk  teeth  are  also  known  in  a  species  of 
Dasypus,  but  with  these  exceptions  Edentates  are,  as  far  as  is 
known,  monophyodont.  In  Glyptodon  the  teeth  are  almost 
divided  into  three  lobes  by  two  deep  grooves  on  each  side. 

The  Aard  Varks  (Orycteropodidae)  are  quite  exceptional 
as  regards  their  teeth,  which  are  cylindrical  in  shape,  and 
are  made  up  of  a  number  of  elongated  denticles  fused  to- 
gether. Each  denticle  contains  a  pulp  cavity  from  which  a 
number  of  minute  tubes  radiate  outwards.  These  teeth  are 
diphyodont  and  somewhat  heterodont,  eight  to  ten  pairs  occur 
in  the  upper  jaw  and  eight  in  the  lower,  but  they  are  not  all  in 
place  at  one  time.  The  last  three  teeth  in  each  jaw  are  not 
preceded  by  milk  teeth1. 

SIRENIA.  The  teeth  of  Sirenia  show  several  very  distinct 
types,  the  least  modified  being  that  of  the  extinct  Hali- 
theriidae,  which  have  large  incisors  in  the  upper  jaw,  and  five 
or  six  pairs  of  tuberculated  grinding  teeth  in  each  jaw,  the 
anterior  ones  being  preceded  by  milk  teeth. 

In  both  the  living  genera  the  dentition  is  monophyodont. 

9  11 

In  Afanatus  the  dentition  is  i  -^  pm  and  m  —  .     The  incisors  are 
,  2 

vestigial,  and  disappear  before  maturity.  The  grinding  teeth 
have  square  enamelled  crowns  marked  by  transverse  tuber- 
culated ridges.  They  are  not  all  present  in  the  jaw  at  the  same 
time.  In  Halicore  the  upper  jaw  bears  a  pair  of  straight  tusk- 
like  incisors ;  in  the  male  these  have  persistent  pulps  and 
project  out  of  the  mouth;  in  the  female  they  soon  cease  to 
grow  and  are  never  cut.  They  are  separated  by  a  long 
diastema  from  the  grinding  teeth  which  have  tuberculated 
crowns  and  are  4-  or  £  in  number,  but  are  not  all  in  place  at 
once.  Several  other  pairs  of  slender  teeth  occur  in  the  young 
animal,  but  are  absorbed  or  fall  out  before  maturity.  In 
Rhytina  teeth  are  altogether  absent. 

1  See  Oldfield  Thomas,  P.  R.  S.t  vol.  XLVII.,  p.  246  (1890). 


426  THE  VERTEBRATE  SKELETON. 

CETACEA. 

ARCHAEOCETI.      Zeuglodon    has    the    following    dentition, 

31  5 

i  ^  c  -  pm  and  m  -=•,  total  36.     The  incisors  and  canines  are 
31  5 

simple  and  conical ;  the  cheek  teeth  are  compressed  and  have 
serrated  cutting  edges  like  those  in  some  seals. 

In  the  MYSTACOCETI,  or  whalebone  whales,  calcified  tooth 
germs  probably  belonging  to  the  milk  dentition  are  present 
in  the  embryo,  but  they  are  never  functional,  and  are  al- 
together absent  in  the  adult.  The  anterior  of  these  germs 
are  simple,  the  posterior  ones  are  originally  complex,  but 
subsequently  split  up  into  simple  teeth  like  those  of  the 
anterior  part  of  the  jaw.  Hence  according  to  Kukenthal, 
who  described  these  structures,  the  Cetacean  dentition  was 
originally  heterodont. 

In  the  living  ODONTOCETI  the  dentition  is  homodont  and 
monophyodont.  In  some  cases  traces  occur  of  a  replacing 
dentition  which  never  comes  to  maturity,  and  renders  it  pro- 
bable that  the  functional  teeth  of  the  Odontoceti  are  really 
homologous  with  the  milk  teeth  of  other  mammals.  Some  of 
the  dolphins  afford  the  apparently  simplest  type  of  mammalian 
dentition  known.  The  teeth  are  all  simple,  conical,  slightly 
recurved  structures,  with  simple  tapering  roots  and  without 
enamel.  The  dentition  is  typically  piscivorous,  being  adapted 
for  seizing  active  slippery  animals  such  as  fish.  The  prey  is 
then  swallowed  entire  without  mastication.  Sometimes  the 
teeth  are  excessively  numerous,  reaching  two  hundred  or  more 
(fifty  to  sixty  on  each  side  of  each  jaw)  in  Pontoporia.  This 
multiplication  of  teeth  is  regarded  by  Kukenthal  as  due  to  the 
division  into  three  parts  of  numbers  of  trilobed  teeth  similar  to 
those  of  some  seals. 

In  the  Sperm  whale,  Physeter,  the  lower  jaw  bears  a  series 
of  twenty  to  twenty-five  stout  conical  recurved  teeth,  while  in 
the  upper  jaw  the  teeth  are  vestigial  and  remain  imbedded  in 
the  gum.  An  extinct  form,  Physodon,  from  the  Pliocene  of 


THE    SKELETON    IN    MAMMALIA.      THE   TEETH.       427 

Europe  and  Patagonia  is  allied  to  the  Sperm  whale,  but  has 
teeth  in  both  jaws.  In  the  Grampus  Orca,  the  teeth  number 
about  ^|,  and  are  very  large  and  strong.  In  some  forms  the 
teeth  are  very  much  reduced  in  number ;  thus  in  Mesoplodon 
the  dentition  consists  simply  of  a  pair  of  conical  teeth  borne 
in  the  mandible.  In  the  Narwhal  Monodon  the  dentition  is 
practically  reduced  to  a  single  pair  of  teeth,  which  lie  horizon- 
tally in  the  maxilla,  and  in  the  female  normally  remain  perma- 
nently in  the  alveoli.  In  the  male  the  right  tooth  remains 
rudimentary,  while  the  left  is  developed  into  an  enormous 
cylindrical  tusk  marked  by  a  spiral  groove.  Occasionally  both 
teeth  develop  into  tusks,  and  there  is  reason  for  thinking  that 
two-tusked  individuals  are  generally  or  always  female.  In  the 
extinct  Squalodon  the  dentition  is  decidedly  heterodorit,  and 
the  molars  have  two  roots.  The  dental  formula  is 

i  =-  c  —  pm  —  m  -= ,  total  60. 

It  is  probable  that  the  homodont  condition  of  modern  Odonto- 
ceti  is  not  primitive,  but  due  to  retrogressive  evolution. 

UNGULATA. 

Just  as  in  the  Cetacea  a  piscivorous  dentition  is  most 
typically  developed,  so  the  Ungulata  are,  as  a  group,  the  most 
characteristic  representatives  of  a  herbivorous  dentition  in  its 
various  forms. 

UNGULATA  VERA. 

ARTIODACTYLA.  As  regards  the  living  forms,  the  Artio- 
dactyla  can  be  readily  divided  into  two  groups,  namely  those 
with  bunodont  and  those  with  selenodont  teeth.  It  has,  how- 
ever, been  shown  that  selenodont  teeth  always  pass  through 
an  embryonic  bunodont  stage 1.  The  bunodont  type  is  best  seen 

in  Pigs  and  Hippopotami  and  such  extinct  forms  as  Hyotherium. 

/2 3\      }         43 

In  Hippopotamus  the  dental  formula  is  i  , •  -  -=*  c  -  pm  7^0- 

(1 — o)       1          4       o 

1  J.  Taeker,  "  Fur  Kenntniss  der  Odontogenese  bei  Ungulaten."-  Dorpat, 
1892. 


428  THE  VERTEBRATE  SKELETON. 

The  incisors  and  canines  of  Hippopotamus  are  very  large 
and  grow  continuously.  The  genus  Sus,  which  affords  a  good 
instance  of  an  omnivorous  type  of  dentition,  has  the  regular 

unmodified  Mammalian  dental  formula  i  -  c  -  pin  j  m  -  ,  total 

o       1         4       o 

44.  The  canines,  specially  in  the  male,  are  large  and  have 
persistent  pulps,  and  the  upper  canines  do  not  have  the  usual 
downward  direction  but  pass  outwards  and  upwards.  In  the 
Wart  Hog,  Phacochaerus,  they  are  enormously  large,  but  a 
still  more  extraordinary  development  of  teeth  is  found  in 
Babirussa.  In  the  male  Babirussa  the  canines,  which  are  with- 
out enamel,  are  long,  curved  and  grow  continuously.  Those  of 
the  upper  jaw  never  enter  the  mouth,  but  pierce  the  skin  of 
the  face  and  curve  backwards  over  the  forehead.  The  dental 

21         23 
formula  of  Babirussa  is  i  J  c  ^pm  -m^,  total  34. 

0  1          Jo 

The  Wart  Hog  has  a  very  anomalous  dentition,  for  as 
age  advances  all  the  teeth  except  the  canines  and  last  molars 
show  signs  of  disappearing ;  both  pairs  of  persisting  teeth  are 
however  very  large. 

Various  extinct  Uiigulata  such  as  Anoplotherium  have 
teeth  which  are  intermediate  in  character  between  the  bun- 
odont  and  selenodont  types.  Anoplotherium  has  the  regular 
mammalian  series  of  forty -four  teeth.  The  crowns  of  all  the 
teeth  are  equal  in  height,  and  there  is  no  diastema — an 
arrangement  found  in  no  living  mammal  but  man. 

We  come  now  to  the  selenodont  Artiodactyla. 

The  Tylopoda — camels  (Camelidae)  and  Llamas  (Auchenii- 
dae)  when  young  have  the  full  number  of  incisors,  but  in  the  adult 
the  two  upper  middle  ones  are  lost.  The  molars  are  typically 
selenodont  and  hypsodont1.  In  the  Camel  the  dental  formula 

11        33 

is  i  —  c  ^pm  ^m^,  total  34.    The  upper  incisors,  canines  and 
o       1         2i      o 

first  premolars   of  the  Camel  are  very  small  teeth,   and  the 

1  See  p.  345. 


THE  SKELETON  IN  MAMMALIA.      THE   TEETH.        429 

first  premolar  is  separated  by  a  long  diastema  from  the 
others. 

The  Tragulina  or  Chevrotains  have  no  upper  incisors,  while 
the  canines  are  largely  developed,  especially  in  the  male. 

The  Ruminantia  or  Pecora  are  very  uniform  as  regards 
their  dentition.  The  upper  incisors  are  always  absent,  for 
though  their  germs  are  developed  they  are  reabsorbed  without 
ever  becoming  visible,  and  as  a  rule  the  upper  canines  are 
absent  too,  while  the  lower  canines  are  incisiform.  The 
grinding  teeth  are  typically  selenodont,  and  in  the  lower  jaw 
form  a  continuous  series  separated  by  a  wide  diastema  from 
the  canines.  The  dental  formula  is  usually 

.0      0—1         3      3 


The  canines  are  largely  developed  in  the  male  Muskdeer 
(Moschus)  and  in  Hydropotes. 

PERISSODACTYLA.  The  premolars  and  molars  have  a  very 
similar  structure  and  form  a  continuous  series  of  large 
square  teeth  with  complex  crowns.  The  crowns  are  always 
constructed  on  some  modification  of  the  bilophodont1  plan,  as 
is  easily  seen  in  the  case  of  the  forms  with  brachydont  teeth, 
but  in  animals  like  the  Horse,  in  which  the  teeth  are  very 
hypsodont,  this  arrangement  is  hard  to  trace.  All  four  pre- 
molars in  the  upper  jaw  are  preceded  by  milk  teeth,  while  in 
Artiodactyla  the  first  has  no  milk  predecessors. 

In  the  Tapiridae  the  grinding  teeth  are  brachydont  and 
the  lower  ones  are  typically  bilophodont.  The  last  two  upper 
molars  have  the  transverse  ridges  united  by  an  outer  longi- 

31        43 

tudinal  ridge.     The  dentition  is  i  ^  c  =-  pm  -m-^,  total  42. 

o       1         o       o 

In  some  of  the  extinct  Perissodactyles  such  as  Lophiodon2, 

1  See  p.  345. 

2  According  to  H.  F.  Osborn,  Amer.  Natural.,  xxvi.  p.  763,  a  number  of 
not  very  closely  allied  forms  have  been  included  under  Lophiodon. 


430  THE  VERTEBRATE  SKELETON. 

the  dentition  is  brachydont  and  bilophodont,  the  grinding 
teeth  in  general  resembing  the  posterior  upper  molars  of  the 
Tapir.  The  same  type  of  brachydont  tooth  is  seen  in  Palaeo- 
therium  but  the  transverse  ridges  are  crescentic  instead  of 
straight,  and  are  separated  from  one  another  by  shallow 
valleys  without  cement.  Some  of  the  Palaeotheridae  have  the 
regular  series  of  forty-four  teeth. 

A  complete  series  of  forms  is  known  showing  how  from  the 
simple  brachydont  teeth  of  the  Palaeotheridae,  were  derived 
the  complicated  hypsodont  teeth  of  the  Equidae.  The  increase 
in  depth  of  the  tooth  was  accompanied  by  increase  in  the 
depth  and  complexity  of  the  enamel  infoldings,  and  of  the 
cement  filling  them. 

Both  upper  and  lower  grinding  teeth  of  the  Equidae  are 
much  complicated  by  enamel  infoldings,  but  their  derivation 
from  the  bilophodont  type  can  still  be  recognised.  The 
diastema  in  front  of  the  premolars  is  longer  in  the  living 
Equidae  than  in  their  extinct  allies.  In  the  adult  horse  the 

31         33 

dental    formula   is    i  -  c  -pm-m-,  total  40,    with   often   a 
o       1          66 

vestigial  first  upper  premolar  (fig.  82,  pm  1).  The  last  molar  is 
not  more  complex  than  the  others,  and  in  the  female  the  canine 
is  quite  vestigial.  The  incisors  are  large  and  adapted  for  cutting 
and  have  the  enamel  curiously  folded  in  forming  a  deep  pit. 

30  3 

The  milk  dentition  is  di  -=  dc  -  dpm  - ,  total  24.      The  last 

o         0  6 

milk  premolar  is  not  more  complex  than  the  premolar  that 
succeeds  it.  The  horse  affords  an  excellent  instance  of  a 
typically  herbivorous  type  of  dentition,  the  cutting  incisors, 
reduced  canines  and  series  of  large  square  flat-crowned  grinding 
teeth  being  most  characteristic. 

In  Rhinoceros  the  grinding  teeth  are  much  like  those  of 
Lophiodon,  having  an  outer  longitudinal  ridge  from  which  two 
crescentic  transverse  ridges  diverge.  The  upper  premolars  are 
as  complex  as  the  molars,  and  there  are  no  canines ;  in  some 


THE   SKELETON    IN    MAMMALIA.      THE   TEETH.         431 


,-7 


1.1 


FIG.  82.     PALATAL  ASPECT  OF  THE  CRANIUM  AND  MANDIBLE  OF  A 
DONKEY  (Equus  asinus)  x  i.     (Camb.  Mus.) 


1.  supra-occipital. 

2.  occipital  condyle. 

3.  basi-occipital. 


6.  glenoid  surface. 

7.  vomer. 

i  1,  i  3.     first  and  third  incisors. 

4.  vacuity  representing  the  con-         c.     canine. 

fluent     foramen      lacerum        pml,pm2.    first  and  second  pre 
posterius  and  foramen  la-  molars, 

cerum  medium.  m  1.     first  molar. 

5.  auditory  bulla. 


432  THE  VERTEBRATE  SKELETON. 

species  incisors  also  are  absent.     The  dental  formula  is 
.  (0—2)          0  43 

^0=T)C(0=l)^4m3- 

Among  the  Titanotheriidae  Palaeosyops1  has  very  brachy- 
dont  teeth  whose  crowns  have  been  described  as  buno-selenodont, 
the  inner  pair  of  columns  being  bunodont,  the  outer,  seleno- 
dont.  Similar  grinding  teeth  occur  in  Chalicotherium.  Some 
of  the  Titanotheriidae  have  the  regular  mammalian  series  of 
forty -four  teeth. 

SUBUNGULATA. 

TOXODONTIA.  Nesodon  has  the  regular  dental  formula ; 
its  grinding  teeth  are  rooted  and  the  upper  ones  resemble  those 
of  Rhinoceros.  The  second  upper  and  third  lower  incisors 
form  ever-growing  tusks.  There  is  a  marked  difference  between 
the  deciduous  arid  permanent  dentition.  Astrapotherium  like- 
wise has  large  rooted  cheek  teeth  of  a  rhinocerotic  type,  and 
each  jaw  bears  a  pair  of  permanently  growing  tusks,  those 
of  the  lower  jaw  being  the  canines.  The  dental  formula  is 

10        23 
i  -z  c  -  pm  -  m  — ,  total  28. 
o       I          L       o 

In  Toxodon  the  upper  incisors  and  molars  are  large  and  curved 
and  all  the  teeth  have  persistent  pulps.  In  Typotherium  there 
are  no  tusks,  but  the  upper  incisors  are  chisel-like,  recalling 
those  of  Rodents. 

The  CONDYLARTHRA  have  brachydont,  generally  bunodont 
teeth,  with  the  premolars  simpler  than  the  molars.  They 
generally  have  the  regular  dental  formula. 

HYRACOIDEA.     The  dental  formula  of  Procavia  is  usually 

given  as  i^  c  -pm-m-,  total  34;  in  young  individuals  how- 
ever there  occur  a  second  pair  of  upper  incisors  which  early 
fall  out.  The  upper  incisors  resemble  those  of  Rodents  in 
being  long  and  curved  and  growing  from  persistent  pulps. 

1  C.  Earle,  J.  Ac.  Philad.,  vol.  ix.,  1892,  p.  267. 


THE    SKELETON    IN    MAMMALIA.      THE   TEETH.         433 

They  are  however  triangular  in  transverse  section,  not  rect- 
angular, having  two  antero-lateral  faces  covered  with  enamel 
and  a  posterior  face  without  enamel.  Their  terminations 
are  pointed,  not  chisel-shaped  as  in  Rodents.  The  lower  in- 
cisors (fig.  83,  i  1)  are  pectinate  or  partially  divided  by  vertical 
fissures,  and  the  grinding  teeth  are  of  the  rhinocerotic  type. 

2 


6 


-h-\A 


1.1 

FIG.  83.     SKULL  OF  Procavia  (Dendrohyrax)  dorsalisx%.     (Camb.  Mus.) 

1.  nasal.  5.     jugal. 

2.  parietal.  6.     lachrymal  foramen. 

3.  external  auditory  meatus.  i  1.     first  incisor. 

4.  paroccipital    process    of    the 

exoccipital. 

AMBLYPODA.  Two  of  the  best  known  forms  belonging  to 
this  extinct  group  differ  much  as  regards  dentition.  For  while 
Coryphodon  has  the  regular  dental  formula,  and  the  canines 
of  both  jaws  of  moderate  size,  in  Uintatherium  the  dentition 
is  very  specialised,  there  are  no  upper  incisors,  and  the  upper 
canines  form  a  pair  of  enormous  tusks.  The  grinding  teeth 
form  a  continuous  series  marked  by  V-shaped  ridges  and  the 

01         33 

dental  formula  is  i  ^  c  --  pm  —  m—  total  34. 
o       1         o      o 

PROBOSCIDEA.     The  incisors  are  composed  entirely  of  den- 
tine and  have  the  form  of  conical  tusks  projecting  greatly 
R.  28 


434  THE  VERTEBRATE  SKELETON. 

from  the  mouth.  In  living  forms  they  are  confined  to  the 
upper  jaw,  in  some  species  of  the  extinct  Mastodon  however 
they  occur  in  the  lower  jaw  also.  In  Dinotherium  they  are 
probably  absent  from  the  upper  jaw,  but  form  a  pair  of 
downwardly  and  backwardly-directed  tusks  growing  from  the 
elongated  symphysis  of  the  mandible. 

The  grinding  teeth  in  the  various  Proboscidea  show  a  very 
remarkable  series  of  modifications.  In  Dinotherium  they  are 
bilophodont  or  else  are  marked  by  three  straight  transverse 

.  0  ?      0        23 
ridges.      I  he  dental  tormula   is    *  —  c  -pm-?n~  ,    and  the 

teeth  have  the  normal  method  of  succession.  In  Masto- 
don as  in  Dinotherium  the  grinding  teeth  are  marked  by 
transverse  ridges,  but  the  ridges  are  subdivided  into  conical  or 
mammillary  cusps,  and  similar  cusps  often  occur  between 
the  ridges.  These  cusps  are  covered  with  very  thick  enamel 
and  the  spaces  between  them  are  not  filled  up  with  cement. 
There  are  six  of  these  grinding  teeth  for  each  side  of  each 
jaw  but  only  three  are  in  place  at  once.  The  first  three  are 
milk  teeth  as  they  may  be  succeeded  vertically  by  others. 

In  the  true  Elephants  the  number  and  depth  of  the  enamel 
folds  is  much  increased,  and  the  spaces  between  the  folds  are 
filled    up  with    cement.      A  very  complete  series   of  extinct 
forms  is  known  with  teeth  intermediate  in  character  between 
those  of   Mastodon  and   those   of   the  Mammoth  and  living 
elephants.     The  dental  formula  of  Elephas  is 
,.1.1     0    7     3—4      3 
d*0%0e0dm3=4m3' 

Sir  W.  H.  Flower  describes1  the  mode  of  succession  of  teeth 
in  Elephants  as  follows  :  "  As  regards  the  mode  of  succession 
that  of  modern  Elephants  is  as  before  mentioned  very  peculiar. 
During  the  complete  lifetime  of  the  animal  there  are  but  six 
molar  teeth  on  each  side  of  each  jaw  with  occasionally  a  rudi- 
mentary one  in  front,  completing  the  typical  number  of  seven. 
1  Encyclopedia  Britannica,  article  Mammalia,  p.  424. 


THE   SKELETON    IN    MAMMALIA.      THE   TEETH.          435 

The  last  three  represent  the  true  molars  of  ordinary  mammals, 
those  in  front  appear  to  be  milk  molars  which  are  never  re- 
placed by  permanent  successors,  but  the  whole  series  gradually 
moves  forwards  in  the  jaw,  and  the  teeth  become  worn  away 
and  their  remnants  cast  out  in  front  while  development  of 
others  proceeds  behind.  The  individual  teeth  are  so  large 
and  the  processes  of  growth  and  destruction  by  wear  take 
place  so  slowly,  that  not  more  than  one  or  portions  of  two 
teeth  are  ever  in  place  and  in  use  on  each  side  of  each  jaw 
at  one  time,  and  the  whole  series  of  changes  coincides  with 
the  usual  duration  of  the  animal's  life.  On  the  other  hand 
the  Dinotherium,  the  opposite  extreme  of  the  Proboscidean 
series,  has  the  whole  of  the  molar  teeth  in  place  and  use  at 
one  time,  and  the  milk  molars  are  vertically  displaced  by  pre- 
molars  in  the  ordinary  fashion.  Among  Mastodons  trans- 
itional forms  occur  in  the  mode  of  succession  as  well  as  in 
structure,  many  species  showing  a  vertical  displacement  of 
one  or  more  of  the  milk  molars,  and  the  same  has  been  ob- 
served in  one  extinct  species  of  Elephant  (E.  planifrons)  as 
regards  the  posterior  of  these  teeth." 

In  the  TILLODONTIA  the  grinding  teeth  are  of  Ungulate 
type,  while  the  second  incisors  are  large  and  grow  from  per- 
sistent pulps,  so  as  to  resemble  those  of  Rodents. 

BODKNTIA  have  a  most  characteristic  and  very  constant 
dentition,  the  common  dental  formula  being 

*  r G lpm  (£=1) ml> total  18  or  2a 

The  incisors  always  have  chisel-like  edges  and  persistent 
pulps,  and  are  separated  by  a  wide  diastema  from  the 
premolars.  Canines  are  always  absent,  and  there  are  ge- 
nerally three  grinding  teeth  not  preceded  by  milk  teeth  ; 
their  surface  may  be  grooved,  or  may  be  bunodont.  Teeth 
are  most  numerous  in  the  Duplicidentata  (Hares  and  Rabbits), 

9     A        33 
in  which  the  formula  is  i  y  c  -pm-m^,  total  28,  and  fewest 

28—2 


436 


THE  VERTEBRATE  SKELETON. 


in  Hydromys  and  certain  other  forms,  in  which  the  formula  is 

.10         02 

i  y  c  -:  pm  -  m  - ,  total  1 2.     The  hares   and  rabbits  are   the 


VI 


FIG.  84.     CABNASSIAL  OR  SECTOEIAL  TEETH  OF  CARNIVORA  (from 
FLOWER). 

Upper  sectorial  teeth  of  I.  Felts,  II.  Cams,  III.  Ursus.  1.  anterior, 
2.  middle,  3.  posterior  cusp  of  blade,  4.  inner  lobe  supported  on  distinct 
root,  5.  inner  lobe  posterior  in  position  and  without  distinct  root, 
characteristic  of  the  Ursidae. 

Lower  sectorial  teeth.  1.  Fells,  2.  Cauls,  3.  Herpestes.  1.  anterior, 
2.  posterior  lobe  of  blade,  3.  inner  tubercle,  4.  heel. 


THE   SKELETON    IN   MAMMALIA.      THE   TEETH.          437 

only  rodents  which  have  Avell  developed  deciduous  incisors, 
though  a  vestigial  milk  incisor  has  been  described  in  the 
Mouse  (Mus  musculus).  The  last  upper  molar  of  Hydrochaerus 
is  very  complicated,  its  structure  approaching  that  of  the  teeth 
of  Elephants. 

CARNIVORA  have  the  teeth  rooted  and  markedly  diphyodont 
and  heterodont.  The  canines  are  greatly  developed,  and  the 
incisors  are  small. 

In  CARNIVORA  VERA  the  incisors  are  almost  always  §.  The 
fourth  upper  premolar  and  first  lower  molar  are  differentiated 
as  carnassial  teeth  (see  p.  436),  and  retain  fundamentally  the 
same  characters  throughout  the  suborder.  The  upper  car- 
nassial (fig.  84,  I.  II.  III.)  consists  of  a  more  or  less  compressed, 
commonly  trilobed  blade  borne  on  two  roots,  with  an  inner 
tubercle  borne  on  a  third  root.  The  lower  carnassial  has  only 
two  roots ;  its  crown  consists  of  a  bilobed  blade  with  generally 
an  inner  cusp,  and  a  heel  or  talon  (fig.  84,  4)  behind  the  blade. 

The  most  thoroughly  carnivorous  type  of  dentition  is  seen 
in  the  ^luroidea,  and  especially  in  the  cat  tribe  (Felidae).  In 

31         31 
the  genus  Felis  the  dental  formula  is  i  =  c  •=  pm  -  m  - ,  total  30. 

The  incisors  are  very  small,  so  as  not  to  interfere  with  the 
action  of  the  large  canines,  the  lower  carnassial  is  reduced  to 
simply  the  bilobed  blade  (fig.  84,  IV),  and  the  cheek  teeth  are 
greatly  subordinated  to  the  carnassial.  The  extinct  Machae- 
rodus  has  the  upper  canines  comparable  in  size  to  those  of  the 
Walrus. 

The  Civets  and  Hyaenas  have  a  dentition  allying  them 
closely  to  the  cats.  The  hyaena-like  Proteles  has,  however, 
the  grinding  teeth  greatly  reduced. 

.31         4       2 

In  the  Cynoidea1  the  general  dentition  is  i  =  c  •=  pm  -  m  -=  , 

o     1          4       o 

total  42.     This  differs  from  the  regular  mammalian  dentition 

1  See  T.  H.  Huxley,  "The  dental  and  cranial  characters  of  the 
Cauidae,"  P.  Z.  S.,  1880,  p.  238. 


438 


THE  VERTEBRATE  SKELETON. 


only  in  the  absence  of  the  last  upper  molar.  The  upper 
carnassial  tooth  (fig.  84,  II.)  consists  of  a  larger  middle  and 
smaller  posterior  lobe  with  hardly  any  trace  of  an  anterior 
lobe.  The  lower  carnassial  (fig.  84,  V.)  is  typical,  consisting 
of  a  bilobed  blade  with  inner  cusp  and  posterior  talon. 

The  dentition  of  the  Cynoidea  is  most  closely  linked  with 
that  of  the  Arctoidea  by  means  of  fossil  forms. 

In  the  Arctoidea  the  dentition  is  not  so  typically  carnivorous 


FIG.  85.     MANDIBLE  OF  ISABELLINE  BEAR  (Ursus  isabellinus)  x 
(Camb.  Mus.) 

1.  condyle.  m  1. 

2.  coronoid  process. 
i  1.     first  incisor. 


first  molar.  The  dotted 
line  is  pointing  to  the  pos- 
terior half  of  the  tooth. 


c.     canine. 

pm  1,  pm  2.     first  and  second  pre- 
molars. 


This  specimen  has  only 
three  premolars,  there 
should  be  four. 


THE   SKELETON    IN   MAMMALIA.      THE   TEETH.         439 

as  in  the  ^Eluroidea  and  Cynoidea.      In  the  bears,  Ursidae, 
the  molars  have  broad  flat  tuberculated  crowns  (fig.  85).     The 

31          42 
dental  formula   in  Ursus  is  i  -  c     pm      ra     ,  total  42.     The 


upper  carnassial  (fig.  84,  III.)  differs  from  that  of  the 
roidea  and  Cynoidea  in  having  no  inner  lobe  supported  on  a 
third  root.  In  the  large  group  of  Mustelidae  there  are  gene- 
rally two  molars  in  the  lower  and  one  in  the  upper  jaw.  The 
grinding  teeth  commonly  have  large,  flattened,  more  or  less 
tuberculated  crowns,  and  the  upper  molar  may  be  as  large  or 
much  smaller  than  the  carnassial. 

In    the   CREODONTA  there    are   no  specially    differentiated 
carnassial  teeth. 


pm1 


3 

FIG.  86.     LEFT  MANDIBULAR  RAMUS  OF  THE  SEA  LEOPARD  (Ogmorhinus 
leptonyx)  WITH  THE  ROOTS  OF  THE  TEETH  EXPOSED  x  £.     (Ckmb.  Mus.) 

1.  condyle.  pml,  ^w4.     first  and  fourth  pre- 

2.  coronoid  process.  molars. 
i  3.     third  incisor.                                     m.     molar. 

c.     canine. 

In  the  PINNIPEDIA  the  dentition  differs  considerably  from 
that  of  the  Garni vora  vera.  The  milk  dentition  is  always 
vestigial,  and  the  teeth  are  frequently  absorbed  before  birth. 
There  are  four  premolars  and  one  molar,  forming  an  uniform 
series  of  cheek  teeth,  all  of  which  except  in  the  Walrus  have 
compressed  and  pointed,  never  flattened,  crowns.  There  is 
no  special  carnassial  tooth,  and  the  incisors  are  always  fewer 
than  jj .  In  Otaria  the  dentition  is 

*  9  c  T  Pm  7  m  -      —  >  tot&l  34  or  36. 


440  THE  VERTEBRATE  SKELETON. 

In  the  Walrus  the  upper  canines  form  immense  tusks.  The 
other  teeth  are  all  small  and  one-rooted,  and  the  molars  have 
flat  crowns.  In  the  true  seals  the  dentition  is  strikingly  pis- 
civorous, the  cheek  teeth  often  having  accessory  cusps  (fig.  86). 

The  INSECTIVORA  are  diphyodont  and  heterodont,  having 
well-developed  rooted  teeth.  The  canines  are  usually  weak, 
the  incisors  pointed,  and  those  of  the  two  jaws  often  meet 
like  a  pair  of  forceps.  The  crowns  of  the  molars  are  charac- 
teristically studded  with  short  cusps.  Some  genera,  such  as 
Gymnura  and  the  mole,  Talpa,  have  the  regular  mammalian 
dentition.  In  the  hedgehog,  Erinaceus,  the  dentition  is 

i  -    c  ^  pm  -  m  -,  total  36. 

In  the  genus  Sorex  (Shrews)  the  teeth  differ  in  the  following 
two  marked  respects  from  those  of  most  other  Monodelphia, 
(1)  they  are  monophyodont,  (2)  the  lower  incisors  sometimes 
become  fused  to  the  jaws.  Most  Insectivora  have  square  molar 
teeth,  but  in  Potamogale,  Chrysochloris,  Solenodon  and  the 
Centetidae  the  molar  teeth  are  triangular  in  section.  Four 
molars  occur  in  Centetes. 

In   the    aberrant    genus    Galeopithecus    the    dentition    is 
91          23 
i  ^  c  •=  pm  -  m  K  ,  total  34.     The  upper  incisors  are  placed  at 

G          1  2i  O 

some  distance  from  the  anterior  end  of  the  jaw,  and  the  outer 
upper  incisors  and  canines  of  both  jaws  have  two  roots, — a 
very  unusual  character.  The  lower  incisors  are  deeply  grooved 
or  pectinated  in  the  same  way  as  are  the  lower  incisors  of  Pro- 
cavia.  The  upper  incisors  and  canines  of  both  jaws  bear  many 
cusps,  and  are  very  similar  in  appearance  to  the  cheek  teeth  of 
some  Seals. 

The  dentition  of  the  CHIEOPTERA  is  diphyodont  and  hetero- 
dont, and  the  dental  formula  never  exceeds 

21          33 
i  g  c  -  pm  g  m  3 '  total  38- 


THE   SKELETON   IN   MAMMALIA.      THE  TEETH.        441 

The  milk  teeth  are  very  slender  and  have  sharp  recurved  cusps; 
they  are  quite  unlike  the  permanent  teeth.  The  permanent 
teeth  are  of  two  types.  In  the  Insectivorous  forms  the  molar 
teeth  are  cusped,  and  resemble  those  of  Insectivora.  In  the 
blood-sucking  Vampire  bat  Desmodus,  the  teeth  are  peculiarly 
modified ;  the  canines  and  the  single  pair  of  upper  incisors  are 
much  enlarged  and  exceedingly  sharp,  while  all  the  other 
teeth  are  much  reduced  in  size. 

In  the  Frugivorous  bats  the  molar  teeth  have  nearly  always 
smooth  crowns.  The  dental  formula  in  the  chief  genus  Pteropus 

9     1         32 

is  i  -  c  —  pm  -  m  -  ,  total  34. 
2      1          o       «5 

The  PRIMATES  have  a  diphyodont  and  heterodont  dentition, 
generally  of  an  omnivorous  type,  with  cheek  teeth  adapted  for 
grinding.  The  incisors  are  generally  -|,  and  the  molars,  except 
in  the  Hapalidae,  are  §.  In  the  Lemurs  the  upper  canines 
are  large,  and  the  lower  incisors  slender  and  directed  almost 
horizontally  forwards.  The  Aye  Aye,  Chiromys,  has  the  follow- 
ing singular  dentition  :  i  -  c  ^  pm  -  m  ~  ,  total  18.  The  in- 

1        U  U         o 

cisors  much  resemble  those  of  rodents  having  persistent  pulps, 
and  enamel  only  on  the  anterior  face. 

In  Man    and    in   the  Anthropoid    and   Old    World  Apes 

21         23 
the  dental  formula  is  always    i  -  c  -  pm  -  m  ^ ,  total  32. 

In  the  Cebidae  there  is  an  extra  premolar  in  each  jaw 
bringing  the  number  up  to  36.  In  the  Hapalidae,  as  in  the 
Cebidae,  there  is  a  third  premolar,  but  the  molars  are  reduced 
to  f .  Man  is  the  only  Primate  that  has  the  teeth  arranged 
in  a  continuous  series.  In  all  the  others  there  is  a  gap  or 
diastema  of  larger  or  smaller  size  between  the  incisors  and 
canines.  In  all  except  man  also  the  canines  are  enlarged, 
especially  in  the  males. 


442  THE  VERTEBRATE  SKELETON. 

The  Exoskeletal  structures  of  mammals  may  be  summarised 
in  the  following  table  : 

I.  Epidermal  exoskeletal  structures. 

1.  Hairs  (a)  ordinary  hair, 

(6)  vibrissae  and  bristles, 

(c)   spines   of   hedgehog,   porcupine,   Echidna, 
Centetes,  Acanthomys. 

.        (  of  Manidae, 

2.  Scales  \  , 

[  on  tails  of  rats,  beavers,  &c. 

3.  Horns  of  Rhinoceros. 

4.  Horns  of  Bovine  Ruminants. 

5.  Nails,  claws,  hoofs. 

6.  Spurs  of  male  Ornithorhynchus  and  Echidna. 

7.  Horny  beak  and  teeth  of  Ornithorhynchus. 

8.  Horny  pads  on  jaws  of  Sirenians  and  Ruminants. 

9.  Baleen  of  whales. 
10.  Enamel  of  teeth. 

II.  Dermal  exoskeletal  structures. 

1.  Dentine  and  cement  of  teeth. 

2.  Bony  scutes  of  Armadillos. 

ENDOSKELETOK 

VERTEBRAL  COLUMN. 

CERVICAL  VERTEBRAE. 

The  cervical  vertebrae  of  all  mammals  have  certain  cha- 
racters in  common.  However  long  the  neck  may  be,  the 
number  of  cervical  vertebrae,  with  very  few  exceptions,  is 
seven.  Movable  ribs  are  generally  absent,  and  if  present 
are  small  and  do  not  reach  the  sternum.  The  transverse 
processes  are  generally  wide  but  not  long,  and  are  perforated 
near  the  base  by  the  vertebrarterial  canals,  through  which 
the  vertebral  arteries  pass ;  they  generally  bear  downwardly- 
directed  inferior  lamellae  which  are  sometimes  as  in  the  seventh 
human  cervical  seen  to  ossify  from  centres  distinct  from  those 


THE  SKELETON  IN  MAMMALIA.   VERTEBRAL  COLUMN.   443 

forming  the  rest  of  the  transverse  process,  and  are  really  of 
the  nature  of  ribs.  The  atlas  and  axis  always  differ  much 
from  the  other  vertebrae. 

We  may  pass  now  to  the  special  characters  of  the  cervical 
vertebrae  in  the  different  groups.  In  MONOTREMES  and  MAR- 
SUPIALS the  number  of  cervical  vertebrae  is  always  seven.  With 
the  exception  of  the  atlas  of  Echidna  the  cervical  vertebrae 
of  Monotremes  are  without  zygapophyses.  In.  Monotremes  the 
transverse  processes  ossify  from  centres  distinct  from  that  form- 
ing the  body,  and  remain  suturally  connected  with  the  rest  of 
the  vertebra  until  the  adult  condition  is  reached.  The  method 
of  the  ossification  of  the  atlas  in  Marsupials  varies  considerably, 
thus  in  some  forms  such  as  the  Wombats  (Phascolomys)  there  is 
an  unossified  gap  in  the  middle  of  the  inferior  arch  of  the  atlas, 
which  may  remain  permanently  open ;  in  Thylacinus  this  gap 
is  filled  up  by  a  distinct  heart-shaped  piece  of  bone,  while  in 
Didelphys  and  Perameles  the  atlas  is  ossified  below  in  the  same 
way  as  in  other  mammals.  In  Notoryctes  the  second  to  sixth 
cervical  vertebrae  are  ankylosed  together. 

The  cervical  vertebrae  of  the  EDENTATA  have  some  remark- 
able peculiarities.  In  the  three-fingered  Sloth,  Bradypus, 
there  are  nine  cervical  vertebrae,  all  except  the  last  of  which 
have  their  transverse  processes  perforated  by  the  vertebrar- 
terial  canals.  In  a  two-fingered  sloth,  Choloepus  hqffmanni, 
there  are  only  six  cervical  vertebrae.  In  the  Megatheriidae, 
Anteaters  (Myrmecophagidae),  Pangolins  (Manidae),  and  Aard 
Varks  (Orycteropodidae),  the  cervical  vertebrae  are  normal, 
but  in  the  Armadillos  (Dasypodidae),  and  still  more  in  the 
Glyptodonts,  several  of  them  are  commonly  fused  together. 
The  fusion  affects  not  only  the  centra,  but  also  the  neural 
arches,  so  that  the  neural  canals  form  a  continuous  tube. 

In  the  Glyptodonts  there  is  a  complex  joint  at  the  base  of 
the  neck  to  allow  the  partial  retraction  of  the  head  within  the 
carapace.  This  arrangement  recalls  that  in  Tortoises. 

As  a  rule  the  SIRENIA  possess  seven  short  cervical  vertebrae, 


444 


THE  VERTEBRATE  SKELETON. 


not  fused  together  and  not  presenting  any  marked  peculiarities. 
In  Manatus  however  there  are  only  six  cervical  vertebrae  and 
they  are  very  variable. 

In  the  CETACEA  there  are  invariably  seven  cervical  verte- 
brae, but  they  are  always  very  short  and  are  frequently  even 
before  birth  fused  together  by  their  centra  into  one  continuous 
mass  (see  fig.  67).  Sometimes  the  last  one  or  two  are  free.  In 
the  Rorquals  (Balaenoptera)  however,  the  cervical  vertebrae  are 


1- 


FIG.  87.     CERVICAL  VERTEBRAE  OF  A  YOUNG  FIN  WHALE  (Balaenoptera 

musculus)  x  TV     (Camb.  Mus.) 
1. 


surface  on  the  atlas  for  arti- 
culation with  the  occipital 
condyle  of  the  skull. 

2.  foramen  for  exit  of  the  first 

spinal  nerve. 

3.  upper  transverse  process. 

4.  lower  transverse  process. 


In  the  fresh  specimen  these  two 
transverse  processes  are  united  by 
cartilage,  in  adult  individuals  the 
whole  transverse  process  is  ossified. 

5.  epiphyses  of  centrum. 

6.  neural  spine. 


quite  separate  and  distinct  (fig.  87),  and  in  the  fluviatile  Odon- 
toceti,  Platanista,  Inia,  and  Pontoporia,  and  also  in  Beluga 
and  Monodon,  though  very  short  they  are  free.  In  Physeter 
the  first  vertebra  is  free  while  the  others  are  fused.  An 
odontoid  process  is  not  commonly  present  even  in  Cetaceans 
with  free  cervical  vertebrae,  but  a  very  short  one  occurs  in 
the  Rorquals.  The  cervical  vertebrae  of  Rorquals  give  off 
on  each  side  two  transverse  processes  (fig.  87,  3  and  4)  which 


THE  SKELETON  IN  MAMMALIA.      VERTEBRAL  COLUMN.      445 

enclose  between  them  a  wide  space.     These  processes  are  not 
completely  ossified  till  the  animal  is  adult. 

In  all  UNGULATA  the  number  of  cervical  vertebrae  is  seven. 
Among  the  Artiodactyla  two  forms  of  the  odontoid  process  of 
the  axis  occurs ;  in  the  Suina  and  Tragulina  it  is  conical,  in 
the  Ruminantia  and  Tylopoda  it  is  spout-like  (fig.  88,  4).  The 
atlas  in  the  Suina  and  to  a  less  extent  in  the  Ruminantia  has 


B— fe.- 


FIG.  88. 


A 

ATLAS  (B)  AND  AXIS  (A)  VEBTEBRAE  OF  AN  Ox  (Bos 
taurus)  x  %.     (Camb.  Mus. ) 


8. 


7. 


anterior  opening  of  the  verte- 

brarterial  canal, 
foramen  for  the  exit  of  the 

second  spinal  nerve, 
neural  spine, 
postzygapophysis. 


1.  neural  canal. 

2.  transverse  process. 

3.  surfaces  for  articulation  with 

the    occipital    condyles    of 
the  skull. 

4.  spout-like  odontoid  process. 

5.  hypapophysis. 

long  flattened  transverse  processes,  and  the  remaining  cervical 
vertebrae  are  opisthocoelous.  Those  of  the  Giraffe  and  Llama 
(fig.  103)  are  noticeable  for  their  great  length.  In  the  Tylo- 
poda the  posterior  half  of  the  vertebrarterial  canal  is  confluent 
with  the  neural  canal. 

The  Perissodactyla  have  remarkably  opisthocoelous  cervical 
vertebrae.  Those  of  Macrauchenia  have  the  posterior  half  of 
the  vertebrarterial  canal  confluent  with  the  neural  canal  as  in 
Tylopoda.  In  the  Proboscidea  they  are  short  flattened  discs 
slightly  opisthocoelous ;  the  axis  and  seventh  vertebra  and  to 
a  less  extent  the  sixth  have  high  neural  spines. 


446  THE  VERTEBRATE  SKELETON. 

In  the  RODENTIA  the  atlas  generally  has  broad  wing-like 
transverse  processes,  and  the  axis  a  large  and  long  neural  spine, 
while  the  odontoid  process  is  much  developed.  In  the  Jerboas 
(Dipus)  all  the  cervical  vertebrae  except  the  atlas  are  fused 
together,  a  condition  recalling  that  in  armadillos. 

In  the  CARNIVORA  the  wings  of  the  atlas  are  well  developed 
(tig.  69,  A,  1),  and  it  is  deeply  cupped  for  articulation  with 
the  condyles  of  the  skull.  The  axis  has  a  long  odontoid  process 
and  a  high  compressed  neural  spine  (fig.  69,  B,  4).  The  third 
to  sixth  cervical  vertebrae  have  large  transverse  processes  with 
prominent  perforated  inferior  lamellae,  whose  ventral  margins 
in  the  third  and  fourth  vertebrae  diverge  as  they  pass  back- 
wards, while  in  the  fifth  they  are  parallel  and  in  the  sixth 
convergent.  The  transverse  processes  of  the  seventh  vertebra 
have  no  inferior  lamellae  and  are  not  perforated.  Metapo- 
physes  are  often  developed. 

In  the  INSECTIVORA  the  cervical  vertebrae  vary  considerably. 
The  neural  spines  except  in  the  case  of  the  axis  are  generally 
very  small  and  in  the  Shrews  and  Moles  the  neural  arches 
^re  exceedingly  slender. 

In  the  CHIROPTERA  all  the  cervical  vertebrae  are  broad  and 
short  with  slender  neural'  arches. 

PRIMATES.  In  Man  the  cervical  vertebrae  have  short  blunt 
transverse  processes  and  small  often  bifid  neural  spines.  The 
neural  and  vertebrarterial  canals  are  large.  The  atlas  forms 
a  ring  surrounding  a  large  cavity,  and  has  a  very  slender 
inferior  arch  and  small  transverse  processes.  Traces  of  a  pro- 
atlas  have  been  described  in  Macacus  and  Cynocephalus.  The 
axis  has  a  prominent  spine  and  odontoid  process  and  short 
transverse  processes.  In  most  Primates  the  cervical  vertebrae 
are  very  similar  to  those  of  man,  but  the  inferior  lamellae  of 
the  transverse  processes  are  better  developed.  In  the  Anthro- 
poid Apes  the  neural  spines  are  as  a  rule  much  elongated. 


THE  SKELETON  IN  MAMMALIA.      VERTEBRAL  COLUMN.       447 

THORACO-LUMBAR,  OR  TRUNK  VERTEBRAE. 

In  the  MONOTREMATA  there  are  nineteen  thoraco-lumbar 
vertebrae,  sixteen  (Echidna)  or  seventeen  (Ornithorhynchus) 
of  which  bear  ribs.  The  transverse  processes  are  very  short 
and  do  not  articulate  with  the  ribs,  which  are  united  to  the 
centra  only. 

In  the  MARSUPIALIA  there  are  always  nineteen  thoraco- 
lumbar  vertebrae,  thirteen  of  which  generally  bear  ribs.  The 
lumbar  vertebrae  frequently  have  large  metapophyses  and 
anapophyses,  these  being  specially  well  seen  in  the  Kangaroos 
and  Koala  (Phascolarctus). 

The  EDENTATA  are  very  variable  as  regards  their  trunk 
vertebrae.  The  two  genera  of  Sloths  differ  much  as  regards 
the  number,  for  while  Bradypus  has  only  nineteen,  fifteen  or 
sixteen  of  which  bear  ribs,  Choloepus  has  twenty-seven,  twenty- 
four  of  which  are  thoracic,  and  bear  ribs.  In  Bradypus  a 
small  outgrowth  from  the  transverse  process  articulates  with 
the  neural  arch  of  the  succeeding  vertebra.  In  both  genera 
the  neural  spines  are  all  directed  backwards. 

In  the  Megatheriidae  as  in  the  sloths  the  neural  spines 
are  all  directed  backwards,  and  in  the  lumbar  region  additional 
articulating  surfaces  occur,  better  developed  than  are  those  in 
Bradypus. 

In  the  anteaters  (Myrmecophagidae)  there  are  seventeen 
or  eighteen  thoraco-lumbar  vertebrae,  all  of  which  except  two 
or  three  bear  ribs.  The  posterior  thoracic  and  anterior  lumbar 
vertebrae  articulate  in  a  very  complex  fashion,  second,  third,  and 
fourth  pairs  of  zygapophyses  being  progressively  developed  in 
addition  to  the  ordinary  ones,  as  the  vertebrae  are  followed  back. 

In  the  Armadillos  the  lumbar  vertebrae  have  long  meta- 
pophyses which  project  upwards  and  forwards  and  help  to 
support  the  carapace.  In  Glyptodon  almost  all  the  thoraco- 
lumbar  vertebrae  are  completely  ankylosed  together. 

In  the  Manidae  there  are  no  additional  zygapophyses  but 
the  normal  ones  of  the  lumbar  and  posterior  thoracic  regions 


448          THE  VERTEBRATE  SKELETON. 

are  very  much  developed,  the  postzygapophyses  being  semi- 
cylindrical  and  fitting  into  the  deep  prezygapophyses  of  the 
succeeding  vertebra. 

In  the  SIRENIA  the  number  of  lumbar  vertebrae  is  very 
small ;  in  the  dugong  there  are  nineteen  thoracic  and  four 
lumbar,  and  in  the  manatee  seventeen  thoracic  arid  two  lumbar. 

In  the  CETACEA  the  number  of  thoracic  vertebrae  varies  from 
nine  in  Hyperoodon  to  fifteen  or  sixteen  in  Balaenoptera,  and 
the  number  of  lumbar  vertebrae  from  three  in  Inia  to  twenty- 
four  or  more  in  Delphinus.  The  lumbar  vertebrae  are  often 
very  loosely  articulated  together  and  the  zygapophyses  some- 
times as  in  the  Dolphins  are  placed  high  up  on  the  neural 
spines.  The  centra  are  large,  short  in  the  anterior  region  but 
becoming  longer  behind.  The  epiphyses  are  prominent,  and 
so  are  the  neural  spines  and  to  a  less  extent  the  metapophyses. 
The  transverse  processes  are  well  developed,  anteriorly  they 
arise  high  up  on  the  neural  arch,  but  when  the  vertebral 
column  is  followed  back  they  come  gradually  to  be  placed  lower 
down,  till  in  the  lumbar  region  they  project  from  the  middle  of 
the  centra.  This  can  be  well  traced  in  the  Porpoise  (Phocaena). 
In  the  Physeteridae  the  transverse  processes  of  the  anterior 
thoracic  vertebrae  are  similar  to  those  of  most  Cetacea,  but 
when  followed  back,  instead  of  shifting  their  position  on  the 
vertebrae,  they  gradually  disappear,  and  other  processes 
gradually  arise  from  the  point  where  the  capitulum  of  the  rib 
articulates. 

UNGULATA.  In  the  Ungulata  vera  the  thoraco-lumbar 
vertebrae  are  slightly  opisthocoelous.  The  anterior  thoracic 
vertebrae  commonly  have  exceedingly  high  backwardly-pro- 
jecting  neural  spines  (fig.  89,1) ;  but  those  of  the  lumbar  and 
posterior  thoracic  vertebrae  often  point  somewhat  forwards 
so  that  the  spines  all  converge  somewhat  to  a  point  called  the 
centre  of  motion  (cp.  fig.  101).  In  the  Artiodactyla  there  are 
always  nineteen  thoraco-lumbar  vertebrae,  and  in  the  Perisso- 
dactyla  twenty-three. 


THE  SKELETON  IN  MAMMALIA.  VERTEBRAL  COLUMN.   449 


Procavia  sometimes  has  thirty  thoraco-lumbar  vertebrae,  a 
greater  number  than  occurs  in  any  other  terrestrial  mammal ; 


FIG.  89. 


1.  neural  spine. 

2.  neural  canal. 

3.  prezygapophysis. 

4.  facet  for  articulation  with  the 

tuberculum  of  the  rib. 


FlEST    AND    SECOND    THORACIC   VERTEBRAE    OF   AN    Ox    (BOS 

taunts)  x  £.     (Camb.  Mus. ) 

5.  facet  for  articulation  with  the 

capitulum  of  the  rib. 

6.  postzygapophysis. 

7.  foramen    for    exit    of    spinal 

nerve. 


twenty-two  of  these  are  thoracic  and  eight  lumbar.  In  Phe- 
nacodus  the  convergence  of  the  neural  spines  to  a  centre  of 
motion  is  well  seen. 

In  the  Proboscidea  there  are  twenty-three  thoraco-lumbar 
vertebrae,  of  which  nineteen  or  twenty  bear  ribs. 

In  the  RODKNTIA  there  are  generally  nineteen  thoraco- 
lumbar  vertebrae  but  occasionally  the  number  rises  as  high  as 
twenty-five.  In  the  Hares  (Leporidae)  the  number  is  nineteen, 
R.  29 


450          THE  VERTEBRATE  SKELETON. 

twelve  or  thirteen  of  which  are  thoracic.  The  anterior 
thoracic  vertebrae  have  short  centra  and  high  backwardly- 
directed  neural  spines,  the  lumbar  vertebrae  have  large  for- 
wardly-  and  downwardly-directed  transverse  processes  with 
expanded  ends.  Metapophyses,  anapophyses  and  hypapophyses 
are  all  present.  In  the  Agouti  (Dasyprocta)  the  convergence 
of  the  neural  spines  to  a  centre  of  motion  is  very  strongly 
marked. 

In  the  CARNIVORA  the  trunk  vertebrae  are  nearly  always 
twenty  or  twenty-one  in  number;  in  the  genera  Felis  and 
Canis  thirteen  of  these  are  thoracic  and  seven  lumbar.  The 
anterior  thoracic  vertebrae  have  long  back wardly-p rejecting 
neural  spines,  while  the  posterior  thoracic  and  lumbar  vertebrae 
have  shorter  and  thicker  neural  spines  which  project  slightly 
forwards.  In  the  Pinnipedia  there  is  no  change  in  the  direc- 
tion of  the  neural  spines,  and  anapophyses  are  but  little  deve- 
loped. 

In  the  INSECTIVORA  the  number  of  trunk  vertebrae  varies 
much  from  nineteen — thirteen  thoracic  and  six  lumbar — in 
Tupaia,  to  twenty-four — nineteen  thoracic  and  five  lumbar — 
in  Centetes.  The  development  of  the  various  processes  varies 
in  accordance  with  the  habits  of  the  animals,  being  great  in 
the  active  forms,  slight  in  the  slowly  moving  or  burrowing 
forms.  In  Talpa  and  Galeopithecus  the  inter  vertebral  discs 
of  the  thoraco-lumbar  region  instead  of  being  cartilaginous 
have  ossified  forming  intercentra,  a  condition  met  with  in 
very  few  mammals. 

In  the  CHIROPTERA  there  are  seventeen  or  eighteen  thoraco- 
lumbar  vertebrae,  eleven  to  fourteen  of  which  may  bear  ribs. 
The  development  of  processes  is  slight. 

Among  PRIMATES  the  number  of  trunk  vertebrae  is  gene- 
rally nineteen,  of  which  twelve  to  fourteen  bear  ribs ;  in  man 
and  the  Gorilla  and  Chimpanzee  the  number  is,  however, 
seventeen,  and  in  the  Orang  (Simia)  sixteen.  In  some  of  the 
Lemuroidea  there  are  as  many  as  twenty-three  or  twenty-four. 


THE  SKELETON  IN  MAMMALIA.   VERTEBRAL  COLUMN.   451 

In  most  cases  the  neural  spines  converge  more  or  less  to  a 
centre  of  motion,  and  this  is  especially  marked  in  some  of  the 
Lemurs ;  it  does  not  occur  in  man  and  the  anthropoid  apes. 

SACRAL  AND  CAUDAL  VERTEBRAE. 

At  the  posterior  end  of  the  trunk  in  all  mammals  a 
certain  number  of  vertebrae  are  found  fused  together  forming 
the  sacrum.  But  of  these  only  two  or  three  answer  to  the 
definition  of  true  sacral  vertebrae  in  being  united  to  the  ilia 
by  small  ribs.  The  others  which  belong  to  the  caudal  series 
may  be  called  pseudosacral  vertebrae.  In  different  individuals 
of  the  same  species  it  sometimes  happens  that  different 
vertebrae  are  attached  to  the  pelvis  and  form  the  sacrum. 
Sometimes  even  different  vertebrae  are  attached  to  the  pelvis 
at  successive  periods  in  the  life  history  of  the  individual.  This 
is  owing  to  a  shifting  of  the  pelvis  and  has  been  especially 
well  seen  in  man.  In  young  human  embryos  the  pelvis  is 
at  a  certain  stage  attached  to  vertebra  30,  but  as  develop- 
ment goes  on  it  becomes  progressively  attached  to  the  twenty- 
ninth,  twenty-eighth,  twenty-seventh,  twenty-sixth  and  twenty- 
fifth  vertebrae.  As  the  attachment  to  these  anterior  vertebrae 
is  gained,  the  attachment  to  the  posterior  ones  becomes 
lost,  so  that  in  the  adult  the  pelvis  is  generally  attached 
to  vertebrae  25  and  26.  But  there  are  no  absolutely  pre- 
determined sacral  vertebrae,  as  sometimes  the  pelvis  does  not 
reach  vertebra  25,  remaining  attached  to  vertebrae  26  and  27; 
sometimes  it  becomes  attached  even  to  vertebra  24.  This 
shifting  of  the  pelvis  is  seen  in  Choloepus  in  a  more  marked 
degree  even  than  in  man. 

Of  the  MONOTREMATA,  Omithorhynclius  has  two  sacral  verte- 
brae ankylosed  together,  while  Echidna  has  three  or  four1. 

In  MARSUPIALIA  as  a  rule  only  one  vertebra  is  directly 
united  to  the  ilia,  but  one  or  two  more  are  commonly  fused 
to  the  first.  In  the  Wombats  there  may  be  as  many  as  four 

1  G.  B.  Howes,  Journ.  of  Anat.  and  Phys.  xxvu.,  p.  544. 

29—2 


452  THE  VERTEBRATE  SKELETON. 

or  five  vertebrae  fused  together  in  the  sacral  region.  In 
Notary ctes  there  is  extensive  fusion  in  the  sacral  region,  six 
vertebrae,  owing  mainly  to  the  great  development  of  their 
metapophyses,  being  united  with  one  another,  and  with  the 
ilia,  and  the  greater  part  of  the  ischia. 

In  most  EDENTATA  there  is  an  extensive  fusion  of  verte- 
brae in  the  sacral  region.  This  is  especially  marked  in  the 
Armadillos  and  Megatheriidae,  and  to  a  less  extent  in  the 
Sloths  and  Aard  Yarks. 

In  the  SIRENIA  the  vestigial  pelvis  is  attached  by  ligament 
to  the  transverse  processes  of  a  single  vertebra,  which  hence 
may  be  regarded  as  sacral. 

In  CETACEA  there  is  no  sacrum,  the  vestigial  pelvis  not 
being  connected  with  the  vertebral  column. 

In  most  UNGULATA  the  sacrum  consists  of  one  large  ver- 
tebra united  to  the  ilia,  and  having  a  varying  number  of 
smaller  vertebrae  fused  with  it  behind. 

The  same  arrangement  obtains  in  most  RODENTIA,  but  in 
the  Beavers  (Castoridae)  all  the  fused  vertebrae  are  of  much 
the  same  size,  the  posterior  ones  having  long  transverse 
processes  which  nearly  meet  the  ilia. 

In  CARNTVORA  there  may  be  two  sacral  vertebrae  as  in  the 
Hyaena,  three  as  in  the  Dog,  four  or  five  as  in  Bears  and 
Seals. 

In  INSECTIVORA  from  three  to  five  are  united,  while  in 
many  CHIROPTERA  all  the  sacral  and  caudal  vertebrae  have 
coalesced.  Among  PRIMATES,  in  Man  and  Anthropoid  Apes 
there  are  usually  five  fused  vertebrae  forming  the  sacrum, 
but  of  these  only  two  or  three  are  connected  to  the  ilia  by  ribs. 
In  most  of  the  other  Anthropoidea  there  are  two  or  three 
fused  vertebrae,  and  in  the  Lemuroidea  two  to  five. 

FREE  CAUDAL  VERTEBRAE.  The  free  caudal  vertebrae 
vary  greatly  in  number  and  character.  When  the  tail  is  well 
developed,  the  anterior  vertebrae  are  comparatively  short  and 
broad,  with  well-developed  neural  arches  and  zygapophyses ; 


THE  SKELETON  IN  MAMMALIA.  VERTEBRAL  COLUMN.   453 

but  as  the  tail  is  followed  back,  the  centra  gradually 
lengthen  and  become  cylindrical,  and  at  the  same  time  the 
neural  arches  and  all  the  processes  gradually  become  reduced 
and  disappear,  so  that  the  last  few  vertebrae  consist  of  simple 
rod-like  centra.  Chevron  bones  are  frequently  well-developed. 

Of  the  MONOTREMES  Echidna  has  twelve  caudal  vertebrae, 
two  of  which  bear  irregular  chevron  bones.  In  Ornitho- 
rhynchus  there  are  twenty  or  twenty-one  caudal  vertebrae  with 
well-developed  hypapophyses,  but  no  chevron  bones. 

In  MARSUPIALS  there  is  great  diversity  as  regards  the  tail. 
In  the  Wombat  and  Koala  the  tail  is  small  and  without 
chevron  bones.  In  most  other  Marsupials  it  is  very  long, 
having  sometimes  as  many  as  thirty-five  vertebrae  in  the 
prehensile-tailed  opossums.  In  the  Kangaroos  the  tail  is  very 
large  and  stout.  Chevron  bones  are  almost  always  present,  and 
in  Notoryctes  are  large  and  expanded. 

Most  EDENTATES  have  large  tails  with  well -developed 
chevron  bones.  The  length  of  the  tail  varies  greatly  from  the 
rudimentary  condition  in  Sloths  to  that  in  the  Pangolins,  one 
of  which  has  forty-six  to  forty-nine  caudal  vertebrae — the 
largest  number  in  any  known  mammal.  Chevron  bones  are 
much  developed,  sometimes  they  are  Y-shaped,  sometimes  as  in 
Priodon,  they  have  strong  diverging  processes.  The  caudal 
vertebrae  of  Glyptodonts,  though  enclosed  in  a  continuous 
bony  sheath,  have  not  become  ankylosed  together. 

The  SIRENIA  have  numerous  caudal  vertebrae  with  wide 
transverse  processes.  In  the  CETACEA  also  the  tail  is  much 
developed,  and  the  anterior  vertebrae  have  large  chevron 
bones  and  prominent  straight  transverse  processes ;  the  pos- 
terior caudal  vertebrae,  which  in  life  are  enclosed  in  the  hori- 
zontally expanded  tail  fin,  are  without  transverse  processes. 

In  UNGULATA  the  tail  is  simple,  formed  of  short  cylindrical 
vertebrae,  which  in  living  forms  are  never  provided  with 
chevron  bones.  The  number  of  caudal  vertebrae  varies  from 
four,  sometimes  met  with  in  Procavia,  to  thirty-one  in  the 


454  THE  VERTEBRATE  SKELETON. 

Elephant.  The  tail  is  exceedingly  long  in  Anoplotherium  and 
in  Phenacodus,  in  which  there  are  thirty  caudal  vertebrae. 

In  RODENTIA  the  tail  is  variable.  In  the  Hares,  Guinea 
pig  (Cavia)  and  Capybara  it  is  very  small,  in  Pedetes  and  the 
Beaver  it  is  very  long  and  has  well-developed  chevron  bones. 

Most  of  the  CARNIVORA  except  the  Bears  and  Seals  have 
very  long  tails,  the  greatest  number  of  vertebrae,  thirty-six, 
being  met  with  in  Paradoxurus.  Bears  have  only  eight  to 
ten  caudal  vertebrae.  Chevron  bones  are  not  often  much 
developed. 

In  INSECTIVORA  the  tail  is  very  variable  as  regards  length, 
the  number  of  vertebrae  varying  from  eight  in  Centetes  to 
forty-three  in  Microgale. 

In  CHIROPTERA  the  tail  is  sometimes  quite  rudimentary, 
and  as  in  Pteropus,  composed  of  a  few  coalesced  vertebrae, 
sometimes  it  is  formed  of  a  large  number  of  slender  ver- 
tebrae. 

In  PRIMATES  also  the  tail  is  very  variable.  In  Man  all 
the  four  caudal  vertebrae  are  rudimentary  and  are  fused 
together,  forming  the  coccyx.  In  the  Anthropoid  apes,  too, 
there  are  only  four  or  five  caudal  vertebrae.  In  many 
monkeys  of  both  the  eastern  and  western  hemispheres  the 
tail  is  very  long,  having  thirty-three  vertebrae  in  Ateles,  in 
which  genus  it  is  also  prehensile.  Chevron  bones  are  present 
in  all  Primates  with  well-developed  tails.  In  the  Lemuroidea 
the  number  of  caudal  vertebrae  varies  from  seven  to  twenty- 
nine. 


CHAPTER   XXIII. 

GENERAL   ACCOUNT   OF   THE   SKELETON   IN 
MAMMALIA   (CONTINUED). 

THE    SKULL   AND   APPENDICULAK   SKELETON. 

THE  SKULL. 

MONOTREMATA.  In  both  genera  the  cranium  is  thin -walled, 
has  a  fairly  large  cavity,  and  is  very  smooth  and  rounded  ex- 
ternally. The  sutures  between  many  of  the  bones  early  become 
obliterated  in  a  manner  comparable  to  that  in  birds,  and  the 
facial  portion  of  the  skull  is  much  prolonged. 

In  Echidna  the  face  is  drawn  out  into  a  gradually  tapering 
rostrum,  formed  mainly  by  the  premaxillae,  maxillae  and  nasals. 
The  zygomatic  arch  is  very  weak,  and  the  palate  extends  very 
far  back.  The  tympanic  forms  a  slender  ring.  The  mandible 
is  extremely  slight,  with  no  ascending  portion,  and  but  slight 
traces  of  the  coronoid  process  and  angle.  The  hyoid  has  a 
wide  basi-hyal  and  stout  thyro-hyals,  while  the  anterior  cornua 
are  slender,  and  include  ossified  epi-hyals  and  cerato-hyals. 

In  Ornithorhynchus  the  zygomatic  arch  is  much  stouter 
than  in  Echidna.  The  face  is  produced  into  a  wide  beak, 
mainly  supported  by  the  premaxillae,  between  whose  diverging 
anterior  ends  there  is  a  dumb-bell-shaped  bone.  The  maxillae 


456 


THE  VEKTEBEATE  SKELETON. 


are  flattened  below,  and  each  bears  a  large  horny  tooth,  which 
meets  a  corresponding  structure  borne  on  a  surface  near  the 
middle  of  the  mandible.  The  mandible  is  considerably  stouter 
than  in  Echidna,  but  the  angle  and  coronoid  process  are  but 
little  developed.  The  infra-orbital  foramen  and  the  inferior 
dental  and  mental  foramina  of  the  mandible  are  all  very  large. 


Fro.  90.  HALF  FKONT  viEW1  OF  THE  SKULLS  OF  A  TASMANIAN  WOLF  (Thy- 
lacinus  cynocephalus)  (to  the  left)  x  f ;  AND  OF  A  HAIKY-NOSED 
WOMBAT  (Phascolomys  latifrons)  (to  the  right)  xf.  (Camb.  Mus.) 

7.  coronoid  process  of  the  man- 

dible. 

8.  lachrymal  foramen. 

i.  1.     first  upper  incisor. 
C.    canine. 


premaxilla. 

nasal. 

frontal. 

infra-orbital  foramen. 

lachrymal. 

jugal. 


MARSUPIALIA.  The  skulls  of  the  various  types  of  the 
Marsupials  frequently  bear  a  strong  superficial  resemblance  to 
those  of  some  of  the  different  groups  of  placental  mammals. 
Thus  the  skull  of  the  Dasyuridae  resembles  that  of  the  Carni- 
vora,  the  resemblance  being  most  marked  between  the  skulls  of 

1  The  figure  was  drawn  from  a  photograph  and  the  size  of  the  jaws 
relatively  to  the  cranium  is  exaggerated. 


THE   SKELETON    IN   MAMMALIA.      THE    SKULL.        457 

Thylacinus  and  the  dog.  The  skull  of  Notoryctes  is  strongly  sug- 
gestive of  that  of  an  Insectivore,  and  that  of  other  Marsupials 
such  as  the  wombat,  recalls  equally  the  characteristic  features 
of  a  Rodent's  skull.  But,  however  much  they  may  differ  from 
one  another,  the  skulls  of  all  Marsupials  agree  in  the  following 
respects.  (1)  The  brain  cavity,  and  especially  the  cerebral 
fossa,  has  a  very  small  comparative  size.  (2)  The  nasals  are 
always  large,  and  the  mesethmoid  is  extensively  ossified,  and 
terminated  by  a  prominent  vertical  edge.  (3)  Processes  from 
the  jugal  and  frontal  in  living  forms  never  meet  and  enclose 
the  orbit,  but  the  zygomatic  arch  is  always  complete.  (4)  The 
jugal  always  extends  back  to  form  part  of  the  glenoid  fossa. 
(5)  The  lachrymal  canal  opens  either  external  to  or  upon  the 
margin  of  the  orbit,  and  the  nasal  processes  of  the  premaxillae 
never  quite  reach  the  f rentals.  (6)  The  posterior  part  of  the 
palate  is  commonly  pierced  by  large  oval  vacuities.  (7)  The 
tympanic  is  small  and  never  fused  to  the  bones  of  the 
cranium.  (8)  The  carotid  canal  perforates  the  basisphenoid 
and  not  the  tympanic  bulla.  (9)  The  optic  foramen  and 
sphenoidal  fissure  are  confluent.  (10)  In  every  case  except 
Tarsipes  the  angle  of  the  mandible  is  more  or  less  inflected. 

The  skull  of  the  extinct  Thylacoleo  differs  from  that  of  all 
other  Marsupials  in  the  fact  that  the  postorbital  bar  is  com- 
plete. The  hyoid  is  constructed  on  much  the  same  plan  in  all 
Marsupials.  It  consists  of  a  small  basi-hyal,  a  pair  of  broad 
cerato-hyals,  and  a  pair  of  strong  thyro-hyals.  The  epi-hyals 
and  stylo-hyals  are  generally  unossified. 

EDENTATA.  In  Sloths  (Bradypodidae)  the  sutures  become 
early  obliterated,  the  cranial  portion  of  the  skull  is  rather 
high,  and  the  facial  portion  very  short.  The  lachrymal  is  very 
small,  and  its  canal  opens  outside  the  orbit.  The  zygomatic 
arch  is  incomplete,  and  the  jugal  (fig.  91,  5)  is  curiously  forked, 
but  in  a  manner  differing  in  the  two  genera.  The  premaxillae 
are  very  small, — in  Bradypus  quite  vestigial.  The  mandible  is 
well  developed,  the  angle  being  specially  marked  in  Bradypus. 


458  THE   VERTEBRATE    SKELETON. 

In  Choloepus  the  symphysial  part  is  drawn  out  in  a  somewhat 
spout-like  manner  (fig.  91,  6).  In  both  genera  the  thyro-hyals 
are  ankylosed  with  the  basi-hyal. 


5 

FIG.   91.     SKULL  OF  A   TWO-FINGERED   SLOTH   (Choloepus  didactylus)  x  \. 
(Camb.  Mus.) 

1.  anterior  nares.  4.     angle  of  the  mandible. 

2.  postorbital     process     of    the         5.     jugal. 

frontal.  6.     spout-like  prolongation  of  the 

3.  coronoid  process.  mandible. 

In  Megatherium  the  general  appearance  of  the  skull  is 
distinctly  sloth-like,  but  the  facial  portion  is  more  elongated, 
partly  owing  to  the  development  of  a  prenasal  bone,  and  the 
zygomatic  arch  is  complete.  The  mandible  is  very  deep  in  the 
middle,  and  is  drawn  out  into  a  long  spout-like  process  in  front. 

Anteaters  (Myrmecophagidae)  have  a  much  modified  skull, 
and  this  is  especially  the  case  in  the  Great  Anteater,  Myrme- 
cophaga.  The  skull  is  smooth  and  evenly-rounded,  in  these 
respects  recalling  that  of  Echidna,  but  it  is  longer  and  tapers 
much  more  gradually  than  in  Echidna.  The  occipital  condyles 
are  remarkably  large.  The  premaxillae  are  small,  and  the 
long  rostrum  is  chiefly  composed  of  the  maxillae  and  nasals 
with  the  mesethmoid  and  vomer.  The  zygomatic  arch  is 
incomplete,  and  there  is  no  trace  of  a  separation  between  the 
orbit  and  the  temporal  fossa.  The  palate  is  much  elongated, 


THE    SKELETON   IN   MAMMALIA.      THE   SKULL.         459 

the  ptery golds  meeting  in  the  middle  line  just  like  the  pala- 
tines. The  mandible  is  very  long  and  slender,  there  being  no 
definite  coronoid  process,  and  a  short  and  slight  symphysis. 
The  hyoid  arch  is  noticeable  for  the  length  of  the  anterior 
cornu. 

In  the  Armadillos  (Dasypodidae)  the  skull  varies  a  good 
deal  in  shape,  but  the  facial  portion  is  always  tapering  and 
depressed.  The  zygomatic  arch  is  complete.  In  Dasypus  and 
Chlamydophorus  the  tympanic  bulla  is  well  ossified. 

In  the  Glyptodontidae  the  skull  is  very  short  and  deep ; 
the  zygomatic  arch  is  complete,  and  has  a  long  downwardly 
projecting  maxillary  process.  The  mandible  is  massive,  and 
has  a  very  high  ascending  portion. 

In  the  Manidae  the  skull  is  smooth  and  rounded,  the  zygo- 
matic arch  is  incomplete,  and  the  orbit  is  inconspicuous.  The 
palate  is  long  and  narrow,  but  the  pterygoids  do  not  take  part 
in  its  formation.  The  mandible  is  slightly  developed  and  has 
no  angle  or  coronoid  process. 

In  Orycteropus  the  zygomatic  arch  is  complete,  and  there 
is  a  small  postorbital  process  to  the  frontal.  The  mandible  is 
well-developed,  having  a  coronoid  process  and  definite  ascending 
portion,  and  the  hyoid  is  well  ossified. 

SIRENIA.  The  skull,  and  especially  the  brain  case  of  all 
Sirenia,  is  remarkable  for  the  general  density  of  the  component 
bones,  which,  though  often  very  thick,  are  without  air  sinuses. 
It  is  noticeable  also  for  the  roughness  of  the  bones,  and  the 
irregular  manner  in  which  they  are  united  together. 

The  cranial  cavity  is  decidedly  small,  the  reduction  being 
specially  noticeable  in  the  cerebral  fossa,  which  is  not  much 
larger  than  the  cerebellar  fossa.  The  foramen  magnum  is 
large,  and  the  dorsal  surface  of  the  cranium  narrow.  The 
zygomatic  arch  is  very  strongly  developed,  the  squamosal  (fig. 
92,  4)  being  especially  prominent,  and  being  drawn-out  not  only 
into  the  zygomatic  process,  but  also  into  a  large  post- tympanic 
process  which  articulates  with  the  exoccipital.  At  the  side 


460 


THE  VERTEBRATE  SKELETON. 


of  the  skull  between  the  squamosal,  supra-occipital  and  exocci- 
pital,  there  is  a  wide  vacuity  in  the  cranial  wall,  partially  filled 


.-5 


FIG.  92.     LATEBAL  VIEW  OF  THE  SKULL  OF  Rhytina  stelleri  x  % 
(Brit.  Mus.) 

7. 


frontal, 
parietal, 
zygomatic  process 

squamosal. 
squamosal. 
exoccipital. 
occipital  condyle. 


pterygoid  process  of  the  ali- 

sphenoid. 
of     the        8.    jugal. 

9.     premaxilla. 

10.  angle  of  the  mandible. 

11.  maxilla. 


up  by  the  very  large  periotic,  which  is  aiikylosed  to  the  tym- 
panic, but  is  not  united  to  any  other  bones  of  the  skull.  The 
foramen  lacerum  medium  is  confluent  with  the  foramen  lacerum 
anterius,  and  the  two  together  form  an  enormous  vacuity  on 
the  floor  of  the  skull,  bounded  chiefly  by  the  exoccipital,  basi- 
occipital,  alisphenoid  and  squamosal.  The  jugal  (fig.  92,  8)  is 
large  and  in  Manatus  sends  up  a  strong  process,  which  nearly 
or  quite  meets  the  postorbital  process  of  the  frontal,  completing 
the  orbit.  In  the  other  Sirenia  the  orbit  is  completely  confluent 
with  the  very  large  temporal  fossa.  The  lachrymal  in  Manatus 
is  very  small,  but  is  larger  in  Halicore.  The  premaxillae  (fig. 
92,  9)  are  large,  but  smaller  in  Manatus  than  in  the  other 


THE   SKELETON   IN    MAMMALIA.      THE   SKULL.         461 

genera,  in  all  of  which  they  are  curiously  bent  down  in  front. 
Their  upper  margin  forms  the  anterior  border  of  a  very  large 
aperture  lying  high  on  the  roof  of  the  skull  and  extending 
back  for  a  considerable  distance.  This  aperture  is  formed  by 
the  union  of  the  two  anterior  nares.  The  nasals  are  quite 
vestigial  or  absent,  and  the  iiarial  aperture  is  bounded  above 
by  the  frontals;  in  its  floor  are  seen  the  slender  vomer  and 
large  mesethmoid.  The  palate  is  long  and  narrow,  and  formed 
mainly  by  the  maxillae  ;  behind  it  there  is  a  large  irregular 
process  formed  by  the  union  of  the  palatine,  pterygoid,  and 
pterygoid  plate  of  the  alisphenoid.  The  mandible  is  very 
massive  and  has  a  very  high  ascending  portion,  a  rounded 
angle  (fig.  92,  10),  and  a  prominent  coronoid  process ;  the  two 
rami  are  firmly  ankylosed  together.  The  hyoid  consists  prin- 
cipally of  the  broad  flat  basi-hyal ;  the  anterior  cornua  are  but 
slightly  ossified,  while  the  thyro-hyals  are  not  ossified  at  all. 

CETACEA.  The  skull  in  all  Getacea,  especially  in  the  Odon- 
toceti,  is  a  good  deal  modified  from  the  ordinary  mammalian 
type. 

In  the  ARCHAEOCETI  this  modification  is  less  marked  than 
in  either  of  the  other  suborders.  The  nasals  and  premaxillae 
are  a  good  deal  larger  than  they  are  in  living  forms,  and  the 
anterior  nares  are  placed  further  forward.  The  maxillae  do 
not  extend  back  over  the  frontals,  and  there  is  a  well-marked 
sagittal  crest. 

In  the  MYSTACOCETI  the  skull  is  always  quite  bilaterally 
symmetrical,  and  is  not  so  much  modified  from  the  ordinary 
mammalian  type  as  in  the  Odontoceti.  The  parietals  are  not, 
as  in  the  Odontoceti,  separated  by  a  wide  interparietal,  but 
meet ;  they  are,  however,  hidden  under  the  very  large  supra- 
occipital.  The  nasals  are  developed  to  a  certain  extent,  and 
the  nares,  though  placed  very  far  back  and  near  the  top  of  the 
head,  terminate  forwardly-directed  narial  passages.  Turbinal 
bones  are  also  developed  to  some  extent ;  this  fact,  and  the 
occurrence  of  a  definite  though  small  olfactory  fossa  constituting 


462  THE  VERTEBRATE  SKELETON. 

important  distinctions  from  the  Odontoceti.  The  maxillae  are 
large,  but  do  not  extend  back  to  cover  the  frontals  as  in  the 
Odontoceti.  The  zygomatic  process  of  the  squamosal  is  very 
large.  The  mandibular  rami  are  riot  compressed,  but  are 
rounded  and  arched  outwards,  and  never  meet  in  a  long 
symphysis. 

ODONTOCETI.  The  skull  departs  widely  from  the  ordinary 
mammalian  type.  The  following  description  will  apply  to  any 
of  the  following  genera  of  the  Delphinidae,  Phocaena,  Globi- 
cephalus,  Lagenorhynchus,  Delphinus,  Tursiops,  Proddphinus, 
Sotalia. 

The  upper  surface  of  the  skull  is  more  or  less  asymmetrical. 
The  cerebral  cavity  is  high,  short  and  broad ;  and  formed  mainly 
by  the  cerebral  fossa,  the  olfactory  fossa  being  entirely  absent. 
The  supra-occipital  (fig.  93,  3)  is  very  large,  and  forms  much 
of  the  posterior  part  of  the  roof  of  the  skull.  It  has  the 
interparietal  (fig.  93,  7)  fused  with  it,  and  completely  separates 
the  two  parietals.  The  frontal  (tig.  93,  10)- is  large  and  late- 
rally expanded,  forming  the  roof  of  the  orbit,  but  is  almost 
completely  covered  by  an  extension  of  the  maxilla.  The 
zygomatic  arch  is  very  slender,  and  is  mainly  formed  by  a 
rod-like  process  from  the  jugal  (fig.  93,  15),  the  zygomatic 
process  of  the  squamosal  being  short  and  stout. 

The  nasal  passages  are  peculiarly  modified,  instead  of 
passing  horizontally  forwards  above  the  roof  of  the  mouth, 
they  pass  upwards  and  even  somewhat  backwards  towards 
the  top  of  the  skull  (fig.  93,  23).  They  are  bounded  laterally 
by  two  processes  from  the  premaxillae,  the  left  of  which  is 
shorter  than  the  right.  The  nasal  cavities  are  narrow  and 
without  turbinals  and  the  nasals  (fig.  93,  19)  are  almost  as 
much  reduced  as  in  Sireriia. 

In  front  of  the  nasal  openings  the  face  is  prolonged  as  a 
narrow  beak  or  rostrum  of  varying  length,  formed  by  the 
maxillae  and  premaxillae  surrounding  the  vomer  and  large 
mesethmoid  (fig.  93,  11),  which  sends  forwards  a  long  partially 


THE    SKELETON    IN    MAMMALIA.      THE   SKULL.        463 


21 


18 


FIG.  93.     A,  LATERAL  VIEW,  AND  B,  LONGITUDINAL  SECTION  or  THE  SKULL 
OF  A  YOUNG  CA'ING  WHALE  (Globicephalus  melas)  x  £.     (Brit.  Mus. 

1.  basi-occipital.  13.  periotic. 

2.  exoccipital.  14.  squamosal. 

3.  supra-occipital.  15.  jugal. 

4.  basispbenoid.  16.  vomer. 

5.  alisphenoid.  17.  palatine. 

6.  parietal.  18.  pterygoid. 

7.  interparietal.  19.  nasal. 

8.  presphenoid.  20.  maxilla. 

9.  orbitospbenoid.  21.  premaxilla. 

10.  frontal.  22.  mandible. 

11.  mesethmoid.  23.  anterior  nares. 

12.  tympanic. 


464          THE  VERTEBRATE  SKELETON. 

cartilaginous  process,  and  is  fused  behind  with  the  presphenoid 
(fig.  93,  8).  The  basi-occipital  (fig.  93,  1)  too  is  fused  with 
the  basisphenoid.  The  foramen  rotundum  is  confluent  with 
the  sphenoidal  fissure,  and  the  foramen  ovale  with  the  foramen 
lacerum  medium  and  the  foramen  lacerum  posterius.  The 
palate  is  mainly  formed  by  the  maxillae ;  the  premaxillae  and 
palatines  (fig.  93,  17),  though  both  meet  in  symphyses,  forming 
very  little  of  it.  The  pterygoids  vary  in  size  in  the  different 
genera,  sometimes  as  in  Lagenorhynchus  and  Delphinus  meet- 
ing in  the  middle  line,  sometimes  as  in  Phocaena  and  Globi- 
cephalus  (fig.  93,  18)  being  widely  separated.  The  tympanic 
and  periotic  are  not  fused  together,  and  the  periotic  has 
generally  no  bony  union  with  the  rest  of  the  skull.  The 
mandible  is  rather  slightly  developed,  with  the  rami  straight, 
compressed  and  tapering  to  the  anterior  end.  The  condyle  is 
not  raised  at  all  above  the  edge  of  the  ramus ;  the  angle  is 
rounded  and  the  coronoid  process  is  very  small.  Platanista  has 
a  curiously  modified  skull ;  the  rostrum  and  mandible  are 
exceedingly  long  and  narrow,  and  arising  from  the  maxillae 
are  two  great  plates  of  bone  which  nearly  meet  above. 

In  the  Physeteridae  the  skull  is  raised  into  a  very  promi- 
nent crest  at  the  vertex  behind  the  nares.  In  front  of  this 
in  Hyperoodon  a  pair  of  ridges  occur,  formed  by  outgrowths 
from  the  maxillae.  In  the  old  male  these  ridges  reach  an 
enormous  size  and  almost  meet  in  the  middle  line.  In  Phy 
seter,  the  Sperm  whale,  these  ridges  are  not  developed  ;  the 
maxillae  and  premaxillae  unite  with  the  other  bones  of  the 
crest  enclosing  an  enormous  half  basin-shaped  cavity,  at  the 
base  of  which  are  the  very  asymmetrical  anterior  narial  aper- 
tures. 

In  all  living  Cetacea  the  hyoid  has  the  same  general  shape, 
consisting  firstly  of  a  crescentic  bone  formed  by  the  fusion 
of  the  thyro-hyals  with  the  basi-hyal,  and  secondly  of  the 
anterior  cornu  formed  principally  by  the  strong  stylo-hyal. 

UNGULATA.     None  of  the  distinctive  characters  separating 


THE    SKELETON    IN    MAMMALIA.      THE   SKULL.        465 

the  Ungulata  from  the  other  groups  of  mammals  are  drawn 
from  the  skull.  But  in  the  Ungulata  vera  as  opposed  to  the 
Subungulata  a  distinguishing  feature  is  found  in  the  fact  that 
the  lachrymal  and  jugal  form  a  considerable  part  of  the  side 
of  the  face,  and  that  the  jugal  always  forms  the  anterior  part 
of  the  zygomatic  arch,  the  maxilla  taking  no  part  in  it. 

UNGULATA  VERA. 

ARTIODACTYLA.  The  skull  in  Artiodactyla  differs  from  that 
in  Perissodactyla  in  the  fact  that  the  posterior  end  of  the 
nasal  is  not  expanded  and  there  is  no  alisphenoid  canal. 

The  skulls  in  the  different  groups  of  Artiodactyla  differ 
considerably  from  one  another. 

The  skull  of  the  Pig1  will  be  described  as  illustrative  of  the 
skull  in  the  Suina.  In  the  Pig  as  in  most  Artiodactyla  the 
face  is  bent  sharply  down  on  the  basicranial  axis,  the  com- 
mencement of  the  vomer  being  situated  below  the  mesethmoid 
instead  of  in  front  of  it  as  in  most  skulls.  The  occipital  region 
of  the  skull  is  small,  and  the  line  of  junction  of  the  supra-occi- 
pital and  parietals  is  raised  into  a  prominent  occipital  crest. 
The  parietal  completely  fuses  at  an  early  stage  with  its  fellow, 
and  the  exoccipital  is  drawn  out  into  a  long  paroccipital  process 
(fig.  94,  A,  8).  The  frontal  is  large  and  broad  and  drawn  out 
into  a  small  postorbital  process.  The  lachrymal  too  is  large  and 
takes  a  considerable  part  in  forming  the  side  of  the  face  in  front 
of  the  orbit,  as  does  also  the  jugal,  though  to  a  less  extent. 
The  face  is  long  and  tapers  much  anteriorly.  The  nasals  are 
long  and  narrow,  as  are  the  nasal  processes  of  the  premaxillae, 
which  do  not  however  reach  the  frontals.  A  prenasal  ossicle 
is  developed  in  front  of  the  mesethmoid.  The  palate  is  long 
and  narrow,  the  pterygoid  (fig.  94,  A,  10)  is  small,  but  the 
pterygoid  process  of  the  alisphenoid  is  prominent.  The 
squamosal  is  small  and  has  the  tympanic  fused  with  it ;  the 
tympanic  is  dilated  below,  forming  a  bulla  (fig.  94,  A,  9)  filled 

1  See  W.  K.  Parker,  "On  the  Structure  and  Development  of  the  Skull 
in  the  Pig."  Phil.  Trans,  pp.  289—336,  1874. 

R.  30 


466 


THE  VERTEBRATE  SKELETON. 


1.1 


FIG.  94.    A,  CRANIUM  AND 

1.  jugal. 

2.  postorbital    process     of 

frontal. 

3.  zygomatic    process     of 

squamosal. 

4.  supra-occipital. 

5.  glenoid  cavity. 

6.  occipital  condyle. 

7.  foramen  magnum. 

8.  paroccipital    process    of 

exoccipital. 

9.  tympanic  bulla. 
10.    pterygoid. 


J3,    MANDIBLE    OF   A   PlG    (SUS   SCTOfa)xi. 

(Camb.  Mus.) 

11.     anterior  palatine  foramen, 
the       12.     palatal  plate  of  maxilla. 

13.     coronoid  process, 
the       14.     mandibular  condyle. 

i  1,  i  2,  i  3.    first,  second,  and  third 

incisors, 
c.      canine. 

pm  1,    pm  2,    pm  3,    pm  4.      first, 
second,    third,    and   fourth 
the  premolars. 

ml,  ?w2,  ra3.      first,  second,  and 
third  molars. 


THE   SKELETON   IN   MAMMALIA.      THE  SKULL.       467 

with  cancellous  bone,  and  above  forms  the  floor  of  a  long  up- 
wardly-directed auditory  meatus.  The  mandible  has  a  high 
ascending  portion  and  a  small  coronoid  process  (fig.  94,  B,  13). 
The  hyoid  differs  from  that  of  most  Ungulates,  the  stylo-hyal 
being  very  imperfectly  ossified. 

In  Hippopotamus  the  skull  though  essentially  like  that  of 
the  pig  is  much  modified  in  detail.  The  brain  cavity  is  very 
small,  while  the  jaws  are  immensely  developed.  The  face  con- 
tracts in  front  of  the  orbits  and  then  expands  again  greatly, 
to  lodge  the  enormous  incisor  and  canine  teeth.  The  postorbital 
bar  is  complete  or  nearly  so,  and  the  orbits  project  curiously 
outwards  and  slightly  upwards ;  the  lachrymal  is  thin  and 


FIG.  95.     MANDIBLE  OF  A  HIPPOPOTAMUS  (H.  amphibius)  x  f . 
(Camb.  Mus.) 

The  second  incisor  of  the  left  side  is  missing  and  the  crowns  of  the 
grinding  teeth  are  much  worn. 

1.  condyle.  c.     canine. 

2.  coronoid  process.  pm  3.     third  premolar. 

3.  mental  foramina.  m  1,  m  3.     first  and  third  molar. 
il,  1 2.    first  and  second  incisors. 

30—2 


468  THE  VERTEBRATE  SKELETON. 

much  dilated.  The  squamosal  is  drawn  out  into  a  postglenoid 
process,  and  the  hamular  process  of  the  pterygoid  is  prominent. 
The  tympanic  bulla  is  filled  with  cancellous  bone.  The  mandible 
is  enormously  large,  the  symphysis  is  long,  the  angle  much 
expanded  and  drawn  out  into  a  process  which  projects  outwards 
and  forwards. 

Among  extinct  forms  related  to  the  Suina,  Gyclopidius  is 
noticeable  for  having  large  vacuities  in  the  lachrymo-nasal 
region,  while  Cotylops  has  the  postorbital  bar  complete ;  both 
these  forms  are  from  the  North  American  Miocene. 

In  the  Tylopoda  and  Tragulina  the  skull  resembles  in  most 
respects  that  of  the  Ruminants,  shortly  to  be  described  ;  but  it 
is  allied  to  that  of  the  Suina  in  having  the  tympanic  bulla  filled 
with  cancellous  bone.  The  tympanic  bulla  is  better  developed 
in  the  Tragulina  than  in  most  Ungulates. 

Among  Ruminants,  the  Bovidae,  that  large  group  includ- 
ing the  Oxen,  Sheep,  and  Antelopes,  as  a  rule  have  the  face 
bent  on  the  basicranial  axis  much  as  in  the  Suina.  The 
parietals  are  generally  small  and  early  coalesce,  the  frontals 
are  large  and  are  usually  drawn  out  into  horn  cores,  which  are 
however  absent  in  the  skulls  of  some  domestic  varieties  of  sheep 
and  oxen,  and  also  in  some  of  the  earlier  extinct  forms  of  Bo- 
vidae. These  horn  cores  are  formed  internally  of  cancellous 
bone,  and  on  them  the  true  epidermal  horns  are  borne.  In 
young  animals  there  is  a  distinct  interparietal,  but  this  early 
fuses  with  the  supra-occipital,  and  in  the  oxen  also  with  the 
parietals.  The  occipital  crest  is  generally  well  marked,  but 
in  the  genus  Bos  becomes  merged  in  a  very  prominent  straight 
ridge  running  between  the  two  horn  cores ;  this  ridge,  which 
contains  air  cells  communicating  with  those  in  the  horn  cores,  is 
not  nearly  so  well  marked  in  Bison.  There  is  often,  as  in  Gazella, 
a  vacuity  on  the  side  of  the  face  between  the  nasal,  frontal, 
lachrymal,  and  maxilla,  but  this  is  not  found  in  oxen  or  sheep. 
The  prem axillae  are  small,  the  nasals  are  long  and  pointed, 
and  the  turbinals  are  much  developed.  The  Saiga  antelope 


THE    SKELETON    IN   MAMMALIA.      THE   SKULL.         469 

has  a  curiously  specialised  skull ;  the  nasals  are  absent  or 
have  coalesced  with  the  frontals  and  the  anterior  nares  are 
enormously  large.  In  all  Ruminants  the  lachrymal  is  large 
and  forms  a  considerable  part  of  the  side  of  the  face ;  it  often 
bears  a  considerable  depression,  the  suborbital  or  lachrymal 
fossa,  well  seen  in  most  of  the  smaller  antelopes.  The  post- 
orbital  bar  is  complete,  and  the  orbit  is  prominent  and  nearly 
circular.  The  palatines  and  pterygoids  are  moderately  large, 
and  the  pterygoids  have  a  back wardly-projec ting  hamular  pro- 
cess. The  squamosal  is  small,  but  has  a  postglenoid  process. 
The  tympanic  is  not  fused  to  the  periotic  and  has  a  small  bulla 
not  filled  with  cancellous  bone.  There  is  a  large  paroccipital 
process  to  the  exoccipital  and  the  mandible  has  a  long  slender 
coronoid  process. 

In  the  Cervidae  and  Giraffidae  the  face  is  not  bent  down 
on  the  basicranial  axis  as  it  is  in  the  Bovidae.  The  frontals  are 
drawn  out,  not  into  permanent  horn  cores  as  in  the  Bovidae, 
but  into  short  outgrowths,  the  pedicels,  upon  which  in  the 
Cervidae  long  antlers  are  annually  developed.  These  antlers  are 
outgrowths  of  bone,  and  are  covered  during  development  by 
vascular  integument,  which  dries  up  and  peels  off  when  growth 
is  complete.  Every  year  they  are  detached,  by  a  process  of 
absorption  at  the  base,  and  shed.  They  may  occur  in  both  sexes, 
as  in  the  Reindeer,  but  as  a  rule  they  are  found  only  in  the 
male.  They  are  generally  more  or  less  branched,  and  are  some 
times  of  enormous  size  and  weight,  as  in  the  extinct  Cervus  mega- 
ceros.  In  young  animals  they  are  always  simple,  but  become 
annually  more  and  more  complicated  as  the  animal  grows  older. 

In  the  Giraffe  the  frontals  bear  a  small  pair  of  bony  cores, 
which  are  at  first  distinct,  but  subsequently  become  fused  to 
the  skull.  In  the  allied  Sivatherium,  a  very  large  form  from 
the  Indian  Pliocene,  the  skull  bears  two  pairs  of  bony  out- 
growths, a  pair  of  short  conical  outgrowths  above  the  orbits, 
and  a  pair  of  large  expanded  outgrowths  on  the  occiput. 

The  opening  of  the  lachrymal  canal  is   commonly  double 


470  THE  VERTEBRATE  SKELETON. 

and  the  lachrymal  fossa  is  large  in  the  Cervidae  and  the  Griraf- 
fidae  except  Sivatherium.  The  vacuity  between  the  frontal, 
lachrymal,  maxilla,  and  nasal  is  specially  large. 

The  hyoid  of  Ruminants  is  noticeable  for  the  development 
of  the  anterior  cornua,  which  include  stout  and  short  cerato- 
hyals  and  epi-hyals,  long  and  strong  stylo-hyals  and  large 
tympano-hyals  which  are  more  or  less  imbedded  in  the  tym- 
panics. 

PERISSODACTYLA.  In  the  skull  of  Perissodactyles  an  ali- 
sphenoid  canal  is  found  and  the  nasals  are  expanded  behind. 
Among  the  living  animals  belonging  to  this  group  the  skull  least 
modified  from  the  ordinary  type  is  that  in  Rhinoceros.  In  this 
form  the  skull  is  considerably  elongated,  the  facial  portion  being 
very  large.  The  occipital  region  is  elevated,  but  the  cranial 
cavity  is  small,  the  boundary  line  between  the  occipital  and 
parietal  regions  being  drawn  out  into  a  prominent  crest,  which 
is  occupied  by  air  cells.  There  is  no  postorbital  process  to  the 
frontal,  and  the  orbit  is  completely  confluent  with  the  temporal 
fossa.  The  nasals  are  fused  together  and  are  very  strongly 
developed,  extending  far  forwards,  sometimes  considerably 
beyond  the  premaxillae.  In  some  extinct  species,  such  as  Elas- 
motherium  and  the  Tichorhine  Rhinoceros,  R.  antiquitatis,  the 
mesethmoid  is  ossified  as  far  forwards  as  the  end  of  the  nasals. 
The  nasals  are  arched  and  bear  one  or  two  roughened  surfaces 
to  which  the  great  nasal  horns  are  attached.  The  premaxillae 
are  very  small  and  the  pterygoids  are  slender.  The  palate  is 
long,  narrow,  and  deeply  excavated  behind.  The  postglenoid 
process  of  the  squamosal  is  well  developed,  and  generally 
longer  than  the  paroccipital  process  of  the  exoccipital.  The 
tympanic  and  periotic  are  both  small  and  are  fused  together. 
The  condyle  of  the  mandible  is  very  wide,  the  angle  rounded, 
and  the  coronoid  process  moderately  developed. 

In  the  Titanotheriidae,  a  family  of  extinct  Perissodactyla 
from  the  Miocene  of  North  America,  the  occipital  region  is  much 
elevated,  as  is  also  the  fronto-nasal  region,  the  nasals  (perhaps 


THE  SKELETON   IN   MAMMALIA.      THE   SKULL.         471 

only  in  the  male)  bearing  a  pair  of  blunt  bony  outgrowths, 
Between  these  two  elevated  regions  the  skull  is  much  de- 
pressed. The  cranial,  cavity  is  very  small,  the  orbit  confluent 
with  the  temporal  fossa,  and  the  zygomatic  arch  massive. 

In  Tapirus  the  orbit  and  temporal  fossa  are  confluent. 
The  nasals  are  small,  wide  behind  and  pointed  in  front,  and 
are  supported  by  the  mesethmoid ;  the  anterior  nares  are 
exceedingly  large  and  their  lateral  boundaries  are  entirely 
formed  by  the  maxillae.  The  postglenoid  and  post-tympanic 
processes  of  the  squamosal  are  large.  The  periotic  is  not  fused 
to  the  squamosal  or  to  the  small  tympanic.  The  mandible  is 
large  and  has  the  angle  much  developed  and  somewhat  inflected. 

Palaeotherium,  which  lived  in  early  Tertiary  times,  has  a 
skull  much  like  that  of  the  Tapir,  especially  as  regards  the 
nasal  bones. 

In  the  Horse  and  its  allies  (Equidae)  the  facial  portion  of 
the  skull  is  very  large  as  compared  with  the  cranial  portion, 
the  nasals  and  nasal  cavities  being  specially  large.  In  the 
living  species  of  the  genus  Equus  there  is  no  fossa  between  the 
maxilla  and  lachrymal,  but  it  occurs  in  some  extinct  species. 
The  lachrymal  and  jugal  form  a  considerable  part  of  the  side 
of  the  face ;  and  the  orbit  though  small  is  complete  and  pro- 
minent. The  postorbital  bar  is  formed  by  a  strong  outgrowth 
from  the  frontal,  which  unites  with  a  forward  extension  of  the 
squamosal.  The  squamosal  may  extend  forwards  and  form 
part  of  the  wall  of  the  orbit,  a  very  unusual  feature,  as  in  most 
mammals  the  squamosal  stops  before  the  postorbital  bar.  The 
palate  is  narrow  and  excavated  behind  as  in  Rhinoceros ;  the 
palatines  take  very  little  part  in  its  formation.  The  glenoid 
surface  for  the  articulation  of  the  mandible  is  very  wide.  The 
squamosal  gives  rise  to  small  postglenoid  and  post-tympanic 
processes,  and  the  exoccipital  to  a  large  paroccipital  process. 
The  tympanic  and  periotic  are  ankylosed  together,  but  not  to 
any  other  bones. 

In  the  SUBUNGULATA,  the  lachrymal  and  jugal  do  not  form 


472          THE  VERTEBRATE  SKELETON. 

any  considerable  part  of  the  side  of  the  face,  and  the  maxilla 
commonly  takes  part  in  the  formation  of  the  zygomatic  arch. 

TOXODONTIA.  The  skull  in  the  Toxodontia  shows  several 
Artiodactyloid  features,  while  the  manus  and  pes  are  of  a  more 
Perissodactyloid  type.  The  Artiodactyloid  features  are  (1)  the 
absence  of  an  alisphenoid  canal,  (2)  the  fact  that  the  palate  is 
not  excavated  behind,  and  that  the  palatines  form  a  consider- 
able part  of  it,  and  (3)  the  fusion  of  the  tympanic  to  the 
squamosal  and  exoccipital,  forming  the  floor  of  an  upwardly 
directed  auditory  meatus.  The  frontal  has  a  fairly  well  deve- 
loped postorbital  process,  but  the  orbit  is  confluent  with  the 
temporal  fossa.  The  premaxilla  is  well  developed,  as  is  the  par- 
occipital  process  of  the  exoccipital,  especially  in  Typotherium. 
The  mandible  has  a  rounded  angle  and  a  coronoid  process  of 
moderate  size.  In  Typotherium  the  ascending  portion  is  very 
massive. 

C ONDYLARTHRA.  As  far  as  is  known  the  skull  of  these 
generalised  Ungulates  is  depressed,  and  is  frequently  marked 
by  a  strong  sagittal  crest.  The  cranial  cavity  is  small,  the 
cerebral  fossa  in  Phenacodus  being  exceptionally  small.  The 
orbit  is  completely  confluent  with  the  temporal  fossa. 

HYRACOIDEA.  The  skull  of  Procavia  resembles  that  of 
Perissodactyles  more  than  that  of  any  other  Ungulates,  but 
differs  strongly  in  the  comparatively  small  size  of  its  facial 
portion.  The  posterior  portion  of  the  cranium  is  rather  high, 
the  occipital  plane  being  nearly  vertical.  There  is  a  small 
interparietal.  The  nasals  are  wide  behind,  and  the  zygomatic 
arch  is  strongly  developed,  its  most  anterior  part  being  formed 
by  the  maxilla.  The  jugal  and  parietal  give  rise  to  post- 
orbital  processes  which  sometimes  meet,  but  as  a  rule  the  orbit 
is  confluent  with  the  temporal  fossa;  it  is  very  uncommon 
for  the  parietal  to  give  rise  to  a  postorbital  process,  and  even 
in  Procavia  the  frontal  often  forms  part  of  the  process.  The 
alisphenoid  canal,  and  postglenoid  and  paroccipital  processes 
are  well  developed.  The  tympanic  bulla  is  large  and  the 


THE   SKELETON    IN    MAMMALIA.      THE   SKULL.         473 

periotic  and  tympanic  are  fused  together,  but  not  as  a  rule 
to  the  squamosal.  The  ascending  portion  of  the  mandible  is 
very  high  and  broad,  the  angle  rounded  and  the  coronoid 
process  moderate  in  size.  The  hyoid  is  singular,  there  is  a 
large  flat  basi-hyal  prolonged  laterally  into  two  broad  flattened 
thyro-hyals.  Articulating  with  its  anterior  end  are  two  large 
triangular  cerato-hyals,  which  are  drawn  out  into  two  processes 
meeting  in  the  middle  line. 

AMBLYPODA.  In  the  Uintatheriidae  (Dinocerata)  the  skull 
has  a  very  remarkable  character,  being  long  and  narrow  and 
drawn  out  into  three  pairs  of  rounded  protuberances,  a  small 
pair  on  the  nasals,  a  larger  pair  on  the  maxillae  in  front  of  the 
orbits,  and  the  largest  pair  on  the  parietals.  The  cranial  cavity, 
and  especially  the  cerebral  fossa,  is  extraordinarily  small.  The 
orbit  is  not  divided  behind  from  the  temporal  fossa.  The 
mandible  has  a  prominent  angle,  and  a  long  curved  coronoid 
process ;  its  symphysial  portion  bears  a  curious  flattened  out- 
growth to  protect  the  great  upper  canines. 

In  Coryphodon  the  skull  is  of  a  more  normal  character, 
being  without  the  conspicuous  protuberances.  The  cranial 
cavity  though  very  small  is  not  so  small  as  in  Uintatherium. 

PROBOSCIDEA.  The  character  of  the  skull  in  the  young  ele- 
phant differs  much  from  that  in.  the  old  animal.  In  very  young 
individuals  the  skull  is  of  a  normal  character,  and  the  cranial 
cavity  is  distinctly  large  in  proportion  to  the  bulk  of  the  skull. 
But  as  the  animal  gets  older,  while  its  brain  does  not  grow 
much,  the  size  of  its  trunk  and  especially  of  its  tusks  increases 
greatly ;  and  consequently  the  skull  wall  is  required  to  be  of 
very  great  superficial  extent  in  order  to  afford  space  for  the 
attachment  of  the  muscles  necessary  for  the  support  of  these 
heavy  weights.  This  increase  in  superficial  extent  is  brought 
about  without  much  increase  in  weight  of  bone  by  the  develop- 
ment of  an  enormous  number  of  air  cells  in  nearly  all  the 
bones  of  the  skull ;  sometimes,  as  in  the  case  of  the  frontal, 
separating  the  inner  wall  of  the  bone  from  the  outer,  by  as 


474 


THE  VERTEBRATE  SKELETON. 


much  as  a  foot.  This  development  of  air  cells  is  accompanied 
by  the  obliteration  of  the  sutures  between  the  various  bones. 
The  most  noticeable  point  with  regard  to  the  cranial  cavity 
is  the  comparatively  large  size  of  the  olfactory  fossa.  The 
supra-occipital  (figs.  96  and  97,  9)  is  large — exceedingly  large 
in  the  adult  skull ;  the  parietals  (figs.  96  and  97,  2)  are  also 
very  large.  The  frontals  send  out  small  postorbital  processes, 
but  these  do  not  meet  processes  from  the  small  jugal,  which 


14 


-11 


ml 


FIG.  96.     SKULL  OF  A  YOUNG  INDIAN  ELEPHANT  (Elephas  indicus),  SEEN 

FROM   THE    RIGHT  SIDE,  THE  ROOTS   OF   THE  TEETH  HAVE  BEEN   EXPOSED. 

x  £.     (Camb.  Mus. ) 
1.     exoccipital. 


2.  parietal. 

3.  frontal. 

4.  squamosal. 

5.  jugal. 

6.  premaxilla. 

7.  maxilla. 

9.  supra-occipital. 

13.  basi-occipital. 


14.  postorbital    process     of     the 

frontal. 

15.  lachrymal. 

16.  pterygoid  process  of   the  ali- 

sphenoid. 
i  1.     incisor. 
mm  3.,    mm  4.     third    and    fourth 

milk  molars. 
m  1.     first  molar. 


THE   SKELETON    IN    MAMMALIA.      THE    SKULL. 


475 


forms  only  the  middle  part  of  the  slender  zygomatic  arch,  the 
anterior  part  being  formed  by  the  maxilla.  The  lachrymal 
(fig.  96,  15)  is  small  and  lies  almost  entirely  inside  the  orbit. 
The  anterior  narial  aperture  (fig.  97,  8)  is  wide  and  directed 
upwards,  opening  high  on  the  anterior  surface  of  the  skull.  It 
is  bounded  above  by  the  short  thick  nasals  and  below  by  the 
premaxillae.  The  narial  passage  is  freely  open,  maxillo-tur- 
binals  not  being  developed.  The  palatine  is  well  developed, 
the  pterygoid  is  small  and  early  fuses  with  the  pterygoid 


17 


8--. 


mm4 

FIG.  97.     LONGITUDINAL  SECTION  TAKEN  RATHER   TO   THE  RIGHT  OF  THE 

MIDDLE    LINE    OF    THE    SKULL  OF   A   YOUNG    INDIAN   ELEPHANT    (E. 
Indicus)  x  ^ .     (Camb.  Mus.) 

anterior  nares.  12.     pterygoid. 

periotic.  17.     nasal, 

palatine.  Other  numbers  as  in  Fig.  96. 


8. 
10. 
11. 


process  of  the  alisphenoid.     The  tympanic  is  united  with  the 
periotic  but  not  with  the  squamosal,  and  forms  a  large  auditory 


476  THE  VERTEBRATE  SKELETON. 

bulla.  There  are  no  paroccipital  or  postglenoid  processes. 
The  exoccipital  is  not  perforated  by  the  condylar  foramen, — a 
very  exceptional  condition. 

The  mandible  has  a  high  ascending  portion,  is  rounded  off 
below  and  has  no  angle.  The  symphysial  portion  is  long, 
narrow,  and  spout-like,  and  the  coronoid  process  is  small. 
The  thyro-hyals  are  ankylosed  with  the  basi-hyal,  which  is 
connected  with  the  large  forked  stylo-hyals  by  ligament  only. 

RODENTIA.  The  cranial  cavity  is  depressed,  elongated,  and 
rather  small,  and  the  cerebral  fossa  lies  entirely  in  front  of  the 
cerebellar  fossa.  The  occipital  plane  is  vertical  or  directed 
somewhat  backwards,  and  the  supra-occipital  does  not  form 
much  of  the  roof  of  the  cranium.  The  paroccipital  processes 
of  the  exoccipitals  are  generally  of  moderate  size ;  in  the 
Capybara  (Hydrochaerus),  however,  they  are  very  long,  and 
are  laterally  compressed  and  directed  forwards.  The  parietals 
are  small,  and  often  become  completely  fused  together ;  there 
is  sometimes  a  small  interparietal.  The  frontals  in  most  genera 
have  no  trace  of  a  postorbital  process ;  in  Squirrels,  Marmots 
and  Hares,  however,  one  occurs,  but  in  no  case  does  it  meet  a 
corresponding  process  from  the  zygomatic  arch,  so  the  orbit 
and  temporal  fossa  are  completely  confluent.  In  Hares  the 
postorbital  process  of  the  frontal  is  much  flattened,  and  has 
an  irregular  margin.  The  temporal  fossa  is  always  small,  and 
in  LopJiiomys  is  arched  over  by  plates  arising  respectively 
from  the  parietal  and  jugal  ;  a  secondary  roof  is  thus  partially 
developed  in  a  manner  unique  among  mammals,  but  carried 
to  a  great  extent  in  many  Chelonia.  The  nasal  bones  and 
cavities  are  large,  attaining  their  maximum  development  in 
the  Porcupines  (fig.  98,  1).  The  premaxilla  is  always  very 
large,  and  sends  back  a  long  process  which  meets  the  frontal. 
The  vomer  is  occasionally  found  persisting  in  two  separate 
halves,  a  feature  recalling  the  arrangement  in  Sauropsids.  In 
many  Rodents  there  is  an  enormous  vacuity  at  the  base  of  the 
maxillary  portion  of  the  zygomatic  arch.  It  is  sometimes  as 


THE    SKELETON    IN   MAMMALIA.      THE    SKULL.         477 

large  as  the  orbit,  and  attains  its  maximum  development  in 
the  Capybara  and  other  Hystricomorpha ;  in  the  Marmots, 
Beavers,  and  Squirrels  (Sciuromorpha),  and  in  the  Hares  it  is 
undeveloped.  In  Lagostomus  the  maxilla  bears  an  upwardly 
directed  plate  of  bone,  shutting  off  from  this  vacuity  a  space 
which  is  the  true  infra-orbital  foramen. 

The  zygomatic  arch  is  always  complete,  and  in  many  cases 
the  jugal  extends  back  to  form  part  at  least  of  the  glenoid 

1 


2- 


FIG.  98.     HALF  FRONT  VIEW  OF  THE  SKULL  OF  A  PORCUPINE 
(Hystrix  cristata)x%.     (Camb.  Mus.) 

1.  nasal.  5.     premaxilla. 

2.  maxillo-turbinals.  6.     jugal. 

3.  infra-orbital  vacuity.  i  1.     upper  incisor. 

4.  maxilla. 

surface  for  articulation  with  the  mandible.  In  Coelogenys  the 
jugal  and  maxillary  portion  of  the  zygomatic  arch  is  greatly 
expanded  and  roughened,  and  the  maxillary  portion  encloses  a 
large  cavity.  The  palate  in  Rodents  is  narrow,  and  the  space 
between  the  incisor  and  molar  teeth  passes  imperceptibly 
into  the  sides  of  the  face.  The  anterior  palatine  foramina 
form  long,  rather  narrow  slits  in  this  region.  The  bony 
palate  between  the  grinding  teeth  is  sometimes  as  in  the  Hares 


478  THE  VERTEBRATE  SKELETON. 

very  short,  sometimes  as  in  the  Capybara  very  long.  The 
maxilla  extends  back  beneath  the  orbit  to  unite  with  the 
squamosal.  The  pterygoid  is  always  small,  but  sometimes 
has  a  well-marked  hamular  process  which  in  Hystrix,  Lagos- 
tomus,  and  some  other  genera  unites  with  the  tympanic  bulla. 
The  periotic  is  large,  and  fused  with  the  tympanic,  which 
forms  a  prominent  bulla,  and  is  generally  drawn  out  into  a 
tubular  meatus.  The  bulla  attains  its  maximum  development 
in  Chinchilla  and  Dipus. 

The  mandible  is  narrow  and  rounded  in  front,  the  two 
halves  meeting  in  a  long  symphysis.  The  angle  is  generally 
drawn  out  into  a  long  backwardly-projecting  process,  which  is 
often  pointed  and  directed  upwards.  In  the  Hares  the  angle 
is  rounded.  The  coronoid  process  is  never  large. 

There  are  a  number  of  points  in  which  the  skull  of  the 
Duplicidentata  (Hares  and  Rabbits)  differs  from  that  of  other 
Rodents,  (a)  The  sutures  between  the  basi-occipital  and 
basisphenoid,  and  between  the  basisphenoid  and  presphenoid 
remain  open  throughout  life.  (6)  Much  of  the  maxilla  forming 
the  side  of  the  face  in  front  of  the  orbit  is  fenestrated.  (c)  The 
optic  foramina  are  united  to  form  a  single  hole,  much  as  in 
birds,  (d)  The  coronoid  process  is  slightly  differentiated  from 
the  ascending  portion  of  the  mandible.  The  first  two  of  these 
points  have  been  thought  to  indicate  degradation  of  the 
hares  and  rabbits  as  compared  with  higher  mammals. 

CARNivoRA1.  It  is  characteristic  of  the  skull  in  Carnivora 
that  the  glenoid  fossa  is  deep,  and  the  postglenoid  process 
(fig.  75,  23)  well  developed.  The  condyle  of  the  mandible  is 
much  elongated  transversely.  The  orbit  and  temporal  fossa 
in  the  great  majority  of  forms  communicate  freely,  the  post- 
orbital  bar  being  incomplete. 

CARNIVORA  VERA.  The  axis  of  the  facial  portion  of  the 
skull  is  a  direct  continuation  of  that  of  the  cranial  portion. 

1  See  W.  H.  Flower,  "On  the  value  of  the  characters  of  the  base  of  the 
-cranium  in  the  classification  of  the  order  Carnivora."     P.  Z.  S.  1869,  p.  5. 


THE   SKELETON    IN    MAMMALIA.      THE   SKULL.         479 

The  cranial  cavity  though  rather  depressed  is  large,  and 
generally  long,  though  in  Cats  it  is  comparatively  short  and 
wide.  The  occipital  plane  is  nearly  vertical,  and  the  exocci- 
pitals  are  developed  into  fairly  prominent  paroccipital  processes. 
The  interparietal  is  commonly  distinct,  and  the  parietals  unite 
in  a  long  sagittal  suture,  which  is  often  developed  into  a  crest. 
The  nasals  (fig.  73,  4)  are  well  developed,  especially  in  Cats,  and 
the  nasal  processes  of  the  premaxillae  do  not  nearly  reach  the 
frontals.  A  considerable  part  of  the  palate  is  formed  by  the 
palatine,  and  the  maxillary  portion  is  pierced  by  rather  long 
anterior  palatine  foramina.  The  pterygoid  has  a  hamular 
process.  The  zygomatic  arch  is  strong,  especially  in  Cats. 
Postorbital  processes  are  developed  on  the  frontal  (fig.  73, 
10)  and  jugal,  but  never  form  a  complete  postorbital  bar.  A 
carotid  canal  is  well  seen  in  the  Ursidae,  and  to  a  less  extent 
in  the  Felidae ;  in  the  Canidae  there  is  an  alisphenoid  canal 
(fig.  75,  21). 

The  auditory  bulla  differs  a  good  deal  in  the  different 
groups.  In  the  Bears  (Ursidae)  it  is  not  much  inflated,  and 
is  most  prominent  along  its  inner  border ;  it  is  not  closely  con- 
nected with  the  paroccipital  process.  In  the  Cats  it  is  very 
prominent,  and  its  cavity  is  almost  divided  by  a  septum  into 
two  parts,  the  inner  of  which  contains  the  auditory  ossicles. 
The  paroccipital  process  is  closely  applied  to  the  bulla.  In  the 
Dogs  the  bulla  is  intermediate  in  character  between  that  of 
the  Cats  and  that  of  the  Bears  ;  it  is  partially  divided  by  a 
septum,  and  is  moderately  expanded. 

The  mandible  is  well  developed  with  a  prominent  angle 
(fig.  72,  26),  and  a  large  coronoid  process.  The  hyoid  consists 
of  a  broad  basi-hyal,  a  long  many-jointed  anterior  cornu  and 
short  thyro-hyals  (fig.  72,  33). 

The  skull  in  the  CREODONTA  is  in  most  respects  allied  to 
that  of  the  Canidae,  but  presents  some  ursine  affinities.  The 
tympanic  bulla  is  fairly  prominent,  but  has  no  well-developed 
septum.  The  cranial  cavity  is  very  small  and  narrow,  the 


480          THE  VERTEBRATE  SKELETON. 

zygomatic  arch  standing  away  from  it.  The  temporal  fossa  is 
of  great  size. 

In  the  PINNIPEDIA  the  cranial  cavity  is  large  and  rounded. 
The  skull  is  much  compressed  in  the  interorbital  region,  and 
in  correlation  with  this  compression  the  ethmo-turbinals  are 
little  developed,  while  the  maxillo-turbinals  are  large.  The 
orbit  is  large,  and  the  temporal  fossa  smaller  than  in  the 
Carnivora  vera.  In  the  Walrus  (Trichechus)  the  anterior  part 
of  the  face  is  distorted  by  the  development  of  the  huge  canines. 
The  Otariidae  have  an  alisphenoid  canal.  The  tympanic  bulla 
is  small  in  Otaria,  large  in  the  Phocidae,  and  flattened  in  the 
Walrus.  The  hyoid  is  similar  to  that  in  Carnivora  vera. 

INSECTIVORA.  The  skull  varies  much  in  the  different  mem- 
bers of  the  order  Insectivora,  but  the  following  points  of 
agreement  are  found.  The  cranial  cavity  is  of  small  size,  and 
is  never  much  elevated.  The  facial  part  of  the  skull  is  generally 
considerably  elongated,  and  the  nasals  and  premaxillae  are 
well  developed.  The  zygomatic  arch  is  usually  slender  or 
incomplete,  and  the  coronoid  process  and  angle  of  the  mandible 
are  commonly  prominent. 

In  some  Insectivora,  such  as  Galeopithecus,  Tupaia,  and 
Macroscelides,  the  skull  shows  a  higher  type  of  structure 
than  is  met  with  in  most  members  of  the  order.  In  these 
genera  the  cranial  cavity  is  comparatively  large,  and  the 
occipital  plane  is  nearly  vertical.  The  zygomatic  arch  is  fairly 
strong,  and  the  frontal  and  jugal  give  rise  to  postorbital  pro- 
cesses which  nearly  or  quite  (Tupaia)  meet.  The  tympanic 
bulla  is  well  developed,  and  produced  into  a  tubular  auditory 
meatus,  this  being  specially  well  marked  in  Macroscelides. 

In  the  other  Insectivora  the  cranial  cavity  is  of  smaller 
comparative  size,  and  the  orbit  and  temporal  fossa  are  com- 
pletely confluent,  often  without  any  trace  of  a  postorbital 
bar.  The  occipital  plane  commonly  slopes  forwards.  In 
the  Hedgehogs  (Erinaceidae)  and  Centetidae  the  tympanic  is 
very  slightly  developed,  forming  a  small  ring.  The  zygomatic 


THE   SKELETON   IN   MAMMALIA.      THE   SKULL.        481 

arch  of  Hedgehogs  and  Gymnura  is  very  slender,  the  jugal 
being  but  little  developed  and  the  squamosal  and  maxilla 
meeting  one  another;  in  the  Centetidae  the  jugal  is  absent 
and  the  arch  is  incomplete. 

The  Moles  (Talpidae)  have  an  elongated,  depressed  and 
rounded  skull  with  a  very  slender  zygomatic  arch  formed  by 
the  squamosal  and  maxilla.  The  nasals  are  fused  together, 
and  the  mesethmoid  is  ossified  very  far  forwards.  In  the 
Shrews  (Soricidae)  there  is  no  zygomatic  arch  ;  the  tympanic 
is  ring-like,  and  the  angle  of  the  mandible  is  very  prominent. 
The  hyoid  has  a  transversely  extended  basi-hyal,  a  long 
anterior  cornu  with  three  ossifications,  and  thyro-hyals  which 
are  sometimes  fused  to  the  basi-hyal. 

CHIROPTERA.  In  the  frugivorous  Flying  Foxes  (Ptero- 
pidae)  the  skull  is  elongated,  and  the  cranial  cavity  is  large 
and  arched,  though  considerably  contracted  in  front.  There 
are  commonly  strong  sagittal  and  supra-orbital  crests.  The 
parietals  take  a  great  part  in  the  formation  of  the  walls  of 
the  cranial  cavity,  the  supra-occipital  and  f rentals  being  small. 
The  frontal  is  drawn  out  into  a  long  postorbital  process,  but 
the  zygomatic  arch,  which  is  slender,  and  formed  mainly  by 
the  squamosal  and  maxilla,  gives  rise  to  only  a  small  post- 
orbital  process,  so  that  the  orbit  and  temporal  fossa  are  con- 
fluent. There  is  no  alisphenoid  canal,  and  the  tym panics  are 
very  slightly  connected  with  the  rest  of  the  skull.  The  man- 
dible has  a  large  coronoid  process,  a  rounded  angle,  and  a  trans- 
versely expanded  condyle. 

In  Insectivorous  Bats  the  skull  is  generally  shorter  and 
broader  than  in  the  Pteropidae.  The  cranial  cavity  is  large 
and  rounded,  and  has  thin  smooth  walls.  The  zygomatic 
arch  is  slender,  and  postorbital  processes  are  not  generally 
well  developed.  The  premaxilla  is  generally  small,  sometimes 
absent.  The  tympanics  are  ring-like  and  are  not  connected  with 
the  surrounding  bones.  The  angle  of  the  mandible  is  distinct. 
The  hyoid  in  most  respects  resembles  that  of  the  Insectivora. 

K.  31 


482          THE  VERTEBRATE  SKELETON. 

PRIMATES.  The  characters  of  the  skull  differ  greatly  in 
the  two  suborders  of  Primates,  the  Anthropoidea  and  the 
Lemuroidea. 

In  the  LEMUROIDEA  the  general  relative  proportions  of  the 
cranium  and  face  are  much  as  in  most  lower  mammals,  and  the 
occipital  plane  forms  nearly  a  right  angle  with  the  basicranial 
axis.  The  postorbital  processes  of  the  frontals  are  commonly 
continued  as  a  pair  of  ridges  crossing  the  roof  of  the  cranium 
and  meeting  the  occipital  crest.  Though  the  postorbital  bar 
is  complete,  the  orbit  and  temporal  fossa  communicate  freely 
below  it.  The  lachrymal  canal  opens  outside  the  orbit,  and  the 
lachrymal  forms  a  considerable  part  of  the  side  of  the  face. 
The  tympanic  is  developed  into  a  large  bulla.  The  hyoid 
apparatus  much  resembles  that  of  the  Dog. 

In  the  ANTHROPOIDEA  the  skull  differs  greatly  from  that  in 
the  Lemuroidea.  The  cranial  portion  of  the  skull  is  very 
large  as  compared  with  the  facial  portion,  though  the 
comparative  development  varies,  some  monkeys,  such  as  the 
baboons  (Cynocephali)  having  the  facial  portion  relatively  large. 
The  comparative  size  of  the  jaws  does  not  vary  inversely  with 
the  general  development  of  the  animal,  some  of  the  Cerco- 
pithecidae  having  comparatively  larger  jaws  than  some  of  the 
Cebidae.  The  great  size  of  the  cranial  part  of  the  skull  is 
mainly  due  to  the  immense  development  of  the  cerebral  fossa, 
which  commonly  completely  overlaps  the  olfactory  fossa  in 
front,  and  the  cerebellar  fossa  behind.  This  development  also 
has  the  effect  of  making  the  ethmoidal  and  occipital  planes  lie, 
not  at  right  angles  to  the  basicranial  axis,  but  almost  in  the 
same  straight  line  with  it.  This  is,  however,  not  always  the 
case,  as  the  Howling  Monkey  (Mycetes)  and  also  some  of  the 
very  highest  monkeys,  the  Gibbons  (Hylobates\  have  the  occi- 
pital plane  nearly  vertical  to  the  basicranial  axis.  In  adult 
Man  the  basi-occipital,  exoccipitals  and  supra-occipital  coalesce, 
forming  the  so-called  occipital  bone ;  while  the  basisphenoid, 
presphenoid,  alisphenoids,  orbitosphenoids  and  pterygoids  form 


THE   SKELETON   IN   MAMMALIA.      THE   SKULL.       483 

the  sphenoid  bone.  The  roof  of  the  skull  is  partly  formed 
by  the  large  supra-occipital  and  frontals,  but  mainly  by  the 
parietals  (fig.  99,  1),  which  in  Man  are  of  enormous  extent. 

In  Man  and  in  most  monkeys,  at  any  rate  when  young 
(fig.  99,  B),  the  roof  of  the  skull  is  smooth  and  rounded,  but 
in  many  forms,  such  as  the  Baboons,  in  the  adult  the  supra- 
orbital  and  occipital  ridges  are  much  developed.  In  the  Gorilla 
this  is  also  the  case  with  the  sagittal  crest  (fig.  99,  A,  2).  The 


FIG.  99.     HALF  FRONT  VIEW  OF  THE  SKULLS,  A  OF  AN  OLD,  B  OF  A 
YOUNG  GORILLA  (Gorilla  savagei)  x£.     (Camb.  Mus.) 

1.  parietal.  5.     squamosal. 

2.  sagittal  crest.  6.     maxilla. 

3.  frontal.  7.     external  auditory  meatus. 

4.  supra-orbital  ridge. 

bones  of  the  upper  surface  of  the  cranium  interlock  with  wavy 
outlines.  The  nasals  vary  much  in  length,  being  much  shorter 
in  man  than  in  most  monkeys  ;  they  commonly  become  early 
fused  together,  as  do  also  the  frontals.  The  vomer  is  well 
developed,  and  the  ethmo-turbinal  always  forms  part  of  the 
boundary  of  the  orbit.  There  are  frequently,  as  in  many 
Lemuroidea,  a  pair  of  more  or  less  well-marked  ridges,  cross- 
ing the  roof  of  the  skull  from  the  postorbital  processes  of  the 

31—2 


484          THE  VERTEBRATE  SKELETON. 

f rentals  to  the  occipital  crest.  The  orbit  is  completely  encircled 
by  bone,  and  the  alisphenoid  assists  the  jugal  and  frontal  in 
shutting  it  off  from  the  temporal  fossa,  leaving  however  a 
communication  between  the  two  as  the  sphenomaxillary  fissure. 
In  most  cases  the  frontals  meet  one  another  in  the  middle  line 
between  the  mesethmoid  and  orbitosphenoid,  but  in  Man,  Simia, 
and  some  Cebidae  this  does  not  take  place.  In  nearly  all 
Cebidae  the  parietal  and  jugal  meet  one  another,  separating 
the  frontal  and  alisphenoid  on  the  skull  wall ;  in  Man  and  all 
Old  World  monkeys,  on  the  other  hand,  the  alisphenoid  and 
frontal  meet  and  separate  the  jugal  and  parietal.  The  pre- 
maxillae  nearly  always  send  back  processes  which  meet  the 
nasals.  The  palate  is  rather  short  and  both  the  palatine  and 
the  premaxilla  take  a  considerable  part  in  its  formation.  The 
pterygoid  plate  of  the  alisphenoid  is  decidedly  large,  and  there 
is  no  alisphenoid  canal.  There  is  never  any  great  develop- 
ment either  of  the  paroccipital  process  of  the  exoccipital,  or 
of  the  postglenoid  process  of  the  squamosal.  The  periotic 
and  tympanic  are  always  fused  together ;  in  Cebidae  they 
form  a  small  bulla,  but  a  bulla  is  not  developed  in  any  Old 
World  forms.  The  periotic  is  large,  especially  the  mastoid 
portion,  which  forms  a  distinct  portion  of  the  skull  wall  be- 
tween the  squamosal  and  exoccipital.  In  Man  and  still  more 
in  Old  World  monkeys,  the  external  auditory  meatus  is  drawn 
out  into  a  definite  tube,  whose  lower  wall  is  formed  by  the 
tympanic ;  in  the  Cebidae  the  tympanic  is  ring-like.  The 
perforation  of  the  periotic  by  the  carotid  canal  is  always 
conspicuous. 

The  mandible  is  rather  short  and  broad,  and  the  angle 
formed  by  the  meeting  of  the  two  rami  is  more  obtuse  than  in 
most  mammals.  The  coronoid  process  is  fairly  well  developed, 
and  the  angle  is  more  or  less  rounded.  In  most  Primates  the 
condyle  is  considerably  widened,  but  this  is  not  the  case  in 
Man.  In  Mycetes  the  mandible  is  very  large,  its  ascending 
portions  being  specially  developed.  The  hyoid  of  Primates  is 


THE   SKELETON    IN    MAMMALIA.     AUDITORY    OSSICLES.    485 

remarkable  for  the  large  expanded  basi-hyal,  which  is  generally 
concave  above  and  convex  below.  The  anterior  cornu  is  never 
well  ossified,  but  the  thyro-hyal  is  always  strong.  In  Mycetes 
the  basi-hyal  is  enormously  large,  forming  a  somewhat  globular 
thin-walled  capsule. 

AUDITORY  OSSICLES. 

There  are  in  mammals  four  auditory  ossicles  forming  a 
chain  extending  from  the  fenestra  ovalis  to  the  tympanic 
membrane.  Three  of  these,  the  malleus,  incus  and  stapes, 
are  always  distinct,  while  the  fourth,  the  lenticular,  is  smaller 


FIG.  100.     MALLEUS,  STAPES  AND  INCUS  OF 
A.     MAN.     B.     DOG.     C.     RABBIT.     (After  DOBAN)  x  1. 

1.  head  of  malleus.  5.     manubrium  of  malleus. 

2.  canal  of  stapes.  6.     processus  brevis. 

3.  incus.  7.     lamella. 

4.  processus  longus  (or  gracilis). 

than  the  others  and  is  sometimes  not  distinct.  The  names  are 
derived  from  human  anatomy  and  indicate  in  the  case  of  the 
first  three  a  more  or  less  fanciful  resemblance  respectively  to  a 
hammer,  an  anvil,  and  a  stirrup.  The  ossicles  are  homologous 


486  THE  VERTEBRATE  SKELETON. 

as  a  whole  to  the  hyomandibular  of  fishes  and  to  the  columellar 
chain  of  Sauropsids  and  Amphibians.  The  malleus  is  homo- 
logous to  the  extracolumella  of  Crocodiles  and  the  stapes 
to  the  columella.  The  malleus  when  typically  developed 
consists  of  a  rounded  head  (fig.  100,  1)  which  bears  a  surface 
articulating  with  the  incus,  and  a  short  neck  continued  into  a 
process,  the  manubrium  (fig.  100,  5),  which  comes  into  relation 
with  the  tympanic  membrane.  From  the  junction  of  the  neck 
and  manubrium  two  processes  are  given  off,  a  processus  longus 
or  gracilis  (fig.  100,  4),  which  in  the  embryo  is  continuous 
with  Meek  el's  cartilage,  and  a  processus  brevis  (fig.  100,  6). 
The  incus  generally  consists  of  a  more  or  less  anvil-shaped 
portion  which  articulates  with  the  malleus,  and  of  a  process 
which  is  connected  with  the  stapes  by  the  small  lenticular. 
The  stapes  is  generally  stirrup  shaped,  consisting  of  a  basal 
portion  from  which  arise  two  crura  separated  by  a  space  the 
canal  through  which  a  branch  of  the  pharyngeal  artery  runs 
The  lenticular  is  frequently  cartilaginous  and  sometimes  is 
not  developed  at  all. 

The  above  is  the  arrangement  of  the  auditory  ossicles  met 
with  in  the  higher  Mammalia,  but  in  the  lower  Mammalia 
the  characters  approach  more  nearly  to  those  met  with  in 
Sauropsids. 

In  MONOTREMES  the  ossicles,  though  distinctly  mammalian 
in  character,  show  a  very  low  type  of  development.  The  incus 
is  articulated,  or  often  fused,  with  an  outgrowth  from  the 
head  of  the  malleus.  The  stapes  is  very  much  like  a  reptilian 
columella,  having  a  single  crus  with  no  perforation. 

In  MARSUPIALS  the  ossicles  are  of  a  low  type,  but  not  so 
low  as  the  rest  of  the  skeleton  might  have  led  one  to  expect, 
and  all  or  almost  all  the  points  showing  a  low  grade  of  de- 
velopment may  be  paralleled  among  the  Monodelphia.  The 
lowest  Marsupials  as  regards  the  ossicles  are  the  Peramelidae, 
whose  ossicles  are  of  a  frail  papery  consistence.  The  Didel- 
phyidae  on  the  other  hand  have  the  most  highly  developed 


THE    SKELETON    IN    MAMMALIA.      AUDITORY   OSSICLES.    487 

ossicles,  the  malleus  much  resembling  that  of  many  Insectivores, 
and  the  stapes  having  two  definite  crura  separated  by  a  canal. 

In  EDENTATES  the  character  of  the  ossicles  varies  much. 
In  Sloths  the  stapes  approaches  that  of  Sauropsids  in  its 
narrowness  and  the  slight  trace  of  a  canal ;  this  character 
is  however  still  more  marked  in  Manis,  whose  stapes  is  as 
Sauropsidan  as  that  of  Monotremes,  and  consists  of  a  nearly 
circular  basal  plate  bearing  a  column  which  does  not  show  any 
sign  of  division  into  crura.  The  stapes  of  other  Edentates, 
such  as  anteaters,  aard  varks,  and  most  armadillos,  is  of  a  high 
type  and  has  well-developed  crura.  Priodon  has  a  lower  type 
of  stapes  than  Dasypus  and  Tatusia. 

The  ossicles  of  the  SIRENIA  differ  widely  from  those  of  all 
other  mammals  in  their  great  density  and  clumsy  form. 

In  CETACEA  the  ossicles  are  solid,  though  not  so  solid  as  in 
Sirenia,  and  their  details  vary  much.  The  malleus  is  always 
firmly  fused  to  the  tympanic  by  means  of  the  processus  longus, 
and  the  manubrium  is  very  little  if  at  all  developed.  The 
incus  has  the  stapedial  end  greatly  developed,  and  the  stapes 
has  very  thick  crura  with  hardly  any  canal.  The  ossicles  of 
the  Mystacoceti  are  apparently  less  specialised  than  are  those 
of  the  Odontoceti. 

The  auditory  ossicles  of  the  UNGULATA  do  not  present  any 
characters  common  to  all  the  members  of  the  group. 

Among  Ruminants  they  are  chiefly  remarkable  for  the 
development  of  a  broad  lamellar  expansion  between  the  head 
and  the  processus  longus  of  the  malleus.  In  some  cases  the 
malleus  of  the  foetus  differs  strikingly  from  that  of  the  adult. 
Among  Perissodactyla  the  Rhinoceros  and  Tapir  have  the 
malleus  of  a  low  type,  recalling  those  of  Marsupials ;  while  in 
the  Horse  the  head  is  well  developed,  and  the  malleus  is  of 
a  higher  type. 

The  ossicles  of  Procavia,  which  recall  those  of  the  Equidae, 
are  chiefly  remarkable  for  the  small  size  of  the  body  of  the 
incus.  In  Elephants  the  ossicles  are  large  and  massive. 


488          THE  VERTEBRATE  SKELETON. 

In  the  RODENTIA  (fig.  100,  C)  the  malleus  is  generally 
characterised  by  a  very  broad  manubrium.  In  many  genera 
such  as  Batfiyergus,  and  most  of  the  Hystricomorpha  such  as 
Hystrix,  Chinchilla  and  Dasyprocta,  the  malleus  and  incus  are 
ankylosed  together. 

CARNIVORA.  In  Carnivora  vera  the  most  striking  feature 
of  the  malleus  is  the  occurrence  of  a  broad  lamellar  expan- 
sion between  the  head  and  neck  and  the  processus  longus. 
This  however  does  not  occur  in  some  Yiverridae.  In  the 
Carnivora  vera  the  incus  and  stapes  are  small  as  compared 
with  the  malleus,  but  in  the  Pinnipedia  they  are  large.  In 
the  Pinnipedia  the  auditory  ossicles  have  a  very  dense 
consistence,  and  except  in  the  Otariidae  are  very  large.  The 
stapes  frequently  has  no  canal,  or  only  a  very  small  one. 

In  INSECTIVORA  the  characters  of  the  auditory  ossicles  are 
very  diverse.  Many  forms  such  as  shrews,  moles,  hedgehogs, 
and  the  Centetidae  have  a  low  type  of  malleus  resembling  that 
of  Edentates.  Chrysochloris  has  very  extraordinary  auditory 
ossicles.  The  head  of  the  malleus  is  drawn  out  into  a  great 
club-shaped  process,  the  incus  is  long  and  narrow,  and  differs 
much  from  the  ordinary  type. 

In  CHIROPTERA  the  ossicles  and  especially  the  malleus  much 
resemble  those  of  shrews.  The  stapes  is  always  normal  in 
character,  never  becoming  at  all  columelliform. 

PRIMATES.  In  Man  and  the  Anthropoid  Apes  the  malleus 
has  a  rounded  head,  a  short  neck,  and  the  manubrium,  a 
processus  longus  and  a  processus  brevis.  The  incus  consists  of 
an  anvil-shaped  portion  from  which  arises  a  long  tapering 
process.  The  stapes  has  diverging  crura  and  consequently  a 
wide  canal.  The  crura  in  other  monkeys  do  not  diverge  so 
much  as  in  man  and  anthropoid  apes.  The  New  World  monkeys 
have  no  neck  to  the  malleus. 


THE   SKELETON    IN   MAMMALIA.      THE    STERNUM.      489 
THE  STERNUM1. 

In  MONOTREMES  and  most  MARSUPIALS  the  sternum  does 
not  present  any  characters  of  special  importance.  The  pre- 
sternum  is  strongly  keeled  in  Notoryctes. 

The  sternum  in  EDENTATES  is  very  variable :  in  the  Sloths 
it  is  very  long,  the  mesosternum  of  Choloepus  having  twelve 
segments.  In  the  anteaters  and  armadillos  the  presternum 
is  broad  and  sometimes  as  in  Priodon  strongly  keeled.  In 
Manis  macrura  the  xiphisternum  is  drawn  out  into  a  pair  of 
cartilaginous  processes  about  nine  inches  long. 

In  the  SIRENIA  the  sternum  is  simple  and  elongated,  and 
of  fairly  equal  width  throughout,  in  the  adult  it  shows  no  sign 
of  segmentation.  Its  origin  from  the  union  of  two  lateral 
portions  can  be  well  seen  in  Manatus. 

Two  distinct  types  of  sternum  are  met  with  in  the  CETACEA. 
In  the  Odontoceti  the  sternum  consists  of  a  broad  presternum 
followed  by  three  or  four  mesosternal  segments,  but  with  no 
xiphisternum.  Indications  of  the  original  median  fissure  can 
be  traced,  and  are  very  evident  in  Hyperoodon.  In  the 
Mystacoceti,  on  the  other  hand,  the  sternum  consists  simply 
of  a  broad  flattened  presternum  which  is  sometimes  more  or 
less  heart-shaped,  sometimes  cross-shaped.  Only  a  single  pair 
of  ribs  are  united  to  it. 

The  sternum  in  UNGULATA  is  generally  long  and  narrow  and 
formed  of  six  or  generally  seven  segments.  The  presternum 
is  as  a  rule  small  and  compressed,  often  much  keeled,  especially 
in  the  horse  and  tapir.  The  segments  of  the  mesosternum 
gradually  widen  as  followed  back  and  the  xiphisternum  is 
often  terminated  by  a  cartilaginous  plate. 

In  the  RODENTIA  the  sternum  is  long  and  narrow  and 
generally  has  a  large  presternum,  and  a  xiphisternum  termi- 
nated by  a  broad  cartilaginous  plate. 

1  See  W.  K.  Parker,  Monograph  of  the  shoulder-girdle  and  sternum 
of  the  Vertebrata,  Ray  Soc.  1868. 


490          THE  VERTEBRATE  SKELETON. 

In  the  GARNI VORA,  too,  the  sternum  (fig.  76)  is  long  and 
narrow  and  formed  of  eight  or  nine  pieces,  all  of  nearly  the 
same  size.  The  xiphisternum  generally  ends  in  an  expanded 
plate  of  cartilage. 

In  INSECTIVORA  the  sternum  is  well  developed  but  variable. 
The  presternum  is  commonly  large  and  is  sometimes  as  in  the 
Hedgehog  (Erinaceus)  bilobed  in  front,  sometimes  as  in  the 
Shrew  (Sorex)  trilobed.  It  is  especially  large  in  the  Mole 
(Talpa)  and  is  expanded  laterally  and  keeled  below. 

In  the  CHIROPTERA  the  presternum  is  strongly  keeled  and 
so  is  sometimes  the  mesosternum. 

Among  PRIMATES,  in  Man  and  the  Anthropoid  Apes  the 
sternum  is  rather  broad  and  flattened ;  the  mesosternum 
consists  of  four  segments  which  are  commonly  fused  together 
and  the  xiphisternum  is  imperfectly  ossified. 

THE  RIBS. 

Free  ribs  are  borne  as  a  rule  only  by  the  thoracic  ver- 
tebrae ;  ribs  may  be  found  in  other  regions,  especially  the 
cervical  and  sacral,  but  these  are  almost  always  ankylosed  to 
the  vertebrae.  As  a  general  rule  the  first  thoracic  rib 
joins  the  presternum,  while  the  succeeding  ones  are  attached 
between  the  several  segments  of  the  mesosternum.  Some 
of  the  posterior  ribs  frequently  do  not  reach  the  sternum; 
they  may  then  be  attached  by  fibrous  tissue  to  the  ribs  in 
front,  or  may  end  freely  (floating  ribs).  There  are  generally 
thirteen  pairs  of  ribs,  and  in  no  case  do  they  have  uncinate 
processes. 

In  MONOTREMES  (fig.  102,  B)  each  rib  is  divided  not  into 
two  but  into  three  parts,  an  intermediate  portion  being  inter- 
posed between  the  vertebral  and  sternal  parts.  The  sternal 
ribs  are  well  ossified,  and  some  are  very  broad  and  flat.  The 
intermediate  portions  are  unossified,  those  of  the  anterior  ribs 
are  short  and  narrow,  but  they  become  longer  and  wider 
further  back. 


THE    SKELETON    IN    MAMMALIA.      THE   RIBS.  491 

In  MARSUPIALS  there  are  almost  always  thirteen  pairs 
of  ribs,  whose  sternal  portions  are  very  imperfectly  ossified. 
Notoryctes  has  fourteen  pairs  of  ribs,  eight  of  which  are  float- 
ing: the  first  rib  is  very  stout,  and  is  abruptly  bent  on  itself 
to  join  the  sternum.  It  has  no  distinct  sternal  portion.  All 
the  other  ribs  are  slender. 

Of  the  EDENTATES  the  Sloths  have  very  numerous  ribs ; 
twenty-four  pairs  occur  in  C/ioloepus,  and  half  of  these  reach 
the  sternum.  In  the  Armadillos  there  are  only  ten  or  twelve 
pairs  of  ribs,  but  the  sternal  portions  are  very  strongly  ossified. 
The  first  rib  is  remarkably  broad  and  flat,  and  is  not  divisible 
into  vertebral  and  sternal  portions. 

In  the  SIRENIA  there  are  a  very  large  number  of  ribs 
noticeable  for  their  great  thickness  and  solidity,  but  not 
more  than  three  are  attached  to  the  sternum. 

CETACEA.  In  the  Whalebone  whales  the  ribs  are  remark- 
able for  their  very  loose  connection  both  with  the  vertebral 
column  and  with  the  sternum.  The  capitula  are  scarcely 
developed,  and  the  attachment  of  the  tubercula  to  the  trans- 
verse processes  is  loose.  The  first  rib  is  the  only  one  connected 
with  the  sternum.  In  the  Toothed  whales  the  anterior  ribs 
have  capitula  articulating  with  the  centra,  as  well  as  tubercula 
articulating  with  the  transverse  processes ;  in  the  posterior 
ones,  however,  only  the  tubercula  remain.  Seven  pairs  of 
well-ossified  sternal  ribs  generally  meet  the  sternum.  In  the 
Physeteridae  most  of  the  ribs  are  connected  to  the  vertebrae 
by  both  capitula  and  tubercula. 

In  the  UNGULATA  the  ribs  are  generally  broad  and  flattened, 
and  this  is  especially  the  case  in  the  genera  Bos  and  Bubalus 
(fig.  101,  6).  The  anterior  ribs  are  short  and  nearly  straight, 
and  sternal  ribs  are  well  developed.  The  Artiodactyla  have 
twelve  to  fifteen  pairs  of  ribs,  the  Perissddactyla  eighteen  or 
nineteen,  and  Procavia  twenty  to  twenty-two.  The  Elephant 
has  nineteen  to  twenty-one  pairs,  seven  of  which  may  be  float- 
ing ribs. 


492 


THE   VERTEBRATE   SKELETON. 


CM 


THE  SKELETON  IN  MAMMALIA.   PECTORAL  GIRDLE.  493 

FIG.  101.     SKELETON  OF  A  CAPE  BUFFALO  (Bubalus  coffer). 
The  left  scapula  is  omitted  for  the  sake  of  clearness  xTy.     (Brit.  Mus.) 

1.  premaxilla.  7.  femur. 

2.  nasal.  8.  patella. 

3.  orbit.  9.  tibia. 

4.  neural  spine  of  first  thoracic  10.  metatarsals. 

vertebra.  11.     radius. 

5.  scapula.  12.     metacarpals. 

6.  rib. 

In  the  RODENTIA  there  are  generally  thirteen  pairs  of  ribs, 
which  do  not  present  any  marked  peculiarities. 

The  CARNIVORA  have  thirteen  to  fifteen  pairs  of  ribs, 
whose  vertebral  portions  are  slender,  nearly  straight  and 
subcylindrical,  while  their  sternal  portions  are  long  and 
imperfectly  ossified  (fig.  76,  5).  There  is  nothing  that  calls 
for  special  remark  about  the  ribs,  in  either  INSECTIVOKA  or 
CHIROPTERA. 

PRIMATES.  In  Man  and  the  Orang  (Simia)  there  are  ge- 
nerally twelve  pairs  of  ribs ;  in  the  Gorilla  and  Chimpanzee 
(Antkropopithecus),  and  Gibbons  (Hylobates),  there  are  thirteen, 
in  the  Cebidae  twelve  to  fifteen,  and  in  the  Lemuroidea  twelve 
to  seventeen  pairs.  The  first  vertebral  rib  is  shorter  than  the 
others,  and  the  sternal  ribs  generally  remain  cartilaginous 
throughout  life,  though  in  man  the  first  may  ossify. 

APPENDICULAR  SKELETON. 

THE  PECTORAL  GIRDLE. 

By  far  the  most  primitive  type  of  the  pectoral  or  shoulder 
girdle  is  found  in  the  MONOTREMATA.  The  scapula  (fig.  102, 
A,  1)  is  long  and  recurved,  and  has  only  two  surfaces,  one 
corresponding  to  the  prescapular1  fossa,  the  other  to  the  post- 
scapular1  and  subscapular1  fossae.  The  coracoid  is  a  short  bone 
attached  above  to  the  scapula  and  below  to  the  presternum  ; 
it  forms  a  large  part  of  the  glenoid  cavity.  In  front  of  the 
coracoid  there  is  a  fairly  large  flattened  epicoracoid  (fig.  102,  6); 

1  See  p.  405. 


494 


THE  VERTEBRATE  SKELETON. 


there  is  also  a  large  T-shaped  interdavicle  (fig.  102,  4), 
which  is  expanded  behind  and  rests  on  the  presternum.  The 
clavicles  rest  on  and  are  firmly  united  to  the  anterior  border 
of  the  interclavicle.  This  shoulder  girdle  differs  greatly  from 
that  of  any  other  mammals,  and  recalls  that  of  some  Lacertilia. 
In  MARSUPIALS,  as  in  all  mammals  except  the  Monotremes, 
the  shoulder  girdle  is  much  reduced ;  there  are  no  epicoracoids 

A.  B 


FIG.  102.     A,  SIDE  VIEW,  B,  DORSAL  VIEW  OF  THE  SHOULDER  GIRDLE  AND 

PART    OF   THE    STERNUM   OF  THE    SPINY  ANTEATER  (Echidna 

x  1.     (After  PARKER.) 

1.  scapula.  6.     epicoracoid. 

2.  suprascapula.  7. 

3.  clavicle.  8. 

4.  interclavicle.  9. 

5.  coracoid.  10. 


glenoid  cavity, 
presternum. 
second  sternal  rib. 
second  vertebral  rib. 


and  interclavicle,  and  the  coracoid  forms  simply  a  small  process 
on  the  scapula,  ossifying  from  a  centre  separate  from  that 
giving  rise  to  the  rest  of  the  bone.  The  scapula  has  a  long 
acromion,  and  a  clavicle  is  always  present  except  in  Perameles. 
Unossified  remains  of  the  precoracoids  are  found  at  either  end 
of  the  clavicle.  The  scapula  of  Notoryctes  has  a  very  high 


THE  SKELETON  IN  MAMMALIA.   PECTORAL  GIRDLE.  495 

overhanging  spine,  and  there  is  a  second  strong  ridge  running 
along  the  proximal  part  of  the  glenoid  border. 

The  shoulder  girdle  of  the  EDENTATA  shows  some  very 
curious  variations.  In  Orycteropus  the  scapula  is  of  very 
normal  form  and  the  clavicle  is  well  developed.  In  the  Pan- 
golins and  Anteaters  the  scapula  is  very  broad  and  rounded  ; 
there  is  no  clavicle  in  the  Pangolins,  and  generally  only  a 
vestigial  one  in  Anteaters.  In  Armadillos,  Sloths,  and  Mega- 
theriidae,  the  acromion  is  very  long  and  the  clavicle  is  well 
developed.  In  the  Sloths,  Megatherium,  and  Myrmecophaga,  a 
connection  is  formed  between  the  coracoid,  which  is  unusually 
large,  and  the  coracoid  border  of  the  scapula,  converting  the 
coraco-scapula  notch  into  a  foramen.  In  Bradypus  the 
clavicle  is  very  small,  and  is  attached  to  the  coracoid,  which 
sometimes  forms  a  distinct  bone1. 

In  the  SIRENIA  the  scapula  is  somewhat  narrow  and  curved 
backwards :  the  spine,  acromion,  and  coracoid  process  are 
moderately  developed,  and  there  is  no  clavicle. 

CETACEA.  In  nearly  all  the  Odontoceti  the  scapula  is 
broad  and  somewhat  fan-shaped ;  the  prescapular  fossa  is  much 
reduced,  and  the  acromion  and  coracoid  process  form  flattened 
processes,  extending  forwards  nearly  parallel  to  one  another. 
Some  of  the  Mystacoceti,  such  as  Halaenoptera,  have  a  broad, 
fan-shaped  scapula,  with  a  long  acromion  and  coracoid  process, 
extending  parallel  to  one  another.  Others,  such  as  Balaena, 
have  a  higher  and  narrower  scapula,  with  a  smaller  coracoid 
process. 

In  UNGULATA  the  scapula  is  always  high  and  rather  narrow, 
and  neither  acromion  nor  coracoid  process  is  ever  much  deve- 
loped. In  no  adult  Ungulate  except  Typotherium  is  there  any 
trace  of  a  clavicle,  but  a  vestigial  clavicle  has  been  described 
in  early  embryos  of  sheep2. 

UNGULATA  VERA.     In  the  Ruminantia  the  suprascapular 

1  See  R.  Lydekker,  P.  Z.  S.  1895,  p.  172. 

2  See  H.  Wincza,  Morph.  Jahr.  xvi.  p.  647,  1890. 


496 


THE  VERTEBRATE  SKELETON. 


region  (fig.  103,  5)  is  very  imperfectly  ossified,  and  when  this 
is  removed  the  upper  border  of  the  scapula  is  very  straight 
(fig.  101,  5).  The  spine  is  prominent,  and  generally  has  a 


FIG.  103.     SKELETON  OF  A  LLAMA  (Auchenia  glama)  x 
(Brit.  Mus.) 


hyoid.  6. 

atlas  vertebra.  7. 

seventh  cervical  vertebra.  8. 

scapula.  9. 

imperfectly     ossified      supra-  10. 
scapula. 


olecranon  process  of  ulna. 

metacarpals. 

ilium. 

patella. 

calcaneum. 


fairly  well-marked  acromion.  In  Hippopotamus  the  acromion 
is  fairly  prominent,  but  in  the  other  Suina,  though  the  spine 
is  prominent,  the  acromion  is  not  developed.  The  Perisso- 
dactyla  have  no  acromion,  but  while  the  Equidae  and  Hyra- 
cotherium  have  the  scapula  long  and  slender,  with  the  spine 
very  slightly  developed,  the  other  living  Perissodactyla  have 
the  spine  prominent  and  strongly  bent  back  at  about  the 
middle  of  its  length. 


THE    SKELETON    IN   MAMMALIA.      SHOULDER   GIRDLE.    497 

SUBUNGULA.TA.  Typotherium  (Toxodontia)  differs  from  all 
other  known  Ungulates  in  having  well-developed  clavicles  ; 
its  scapula  has  a  strong  backwardly-projecting  process,  much 
like  that  in  Rhinoceros. 

Phenacodus  (Condylarthra),  has  a  curiously  rounded 
scapula,  with  the  coracoid  and  suprascapular  borders  passing 
imperceptibly  into  one  another.  The  scapula  resembles  that 
of  a  carnivore  more  than  does  that  of  any  existing  Ungulate. 

Procavia  has  a  triangular  scapula  with  a  prominent  spine 
and  no  acromion  ;  there  is  a  large  unossified  suprascapular 
region. 

The  scapula  in  the  Proboscidea  has  a  large  rounded  supra- 
scapular  border  and  a  narrow,  slightly  concave  glenoid  border. 
The  spine  is  large,  and  has  a  prominent  process  projecting 
backwards  from  about  its  middle.  The  spine  lies  towards 
the  front  end  of  the  scapula,  so  that  the  postscapular  fossa  is 
much  larger  than  the  prescapular  fossa. 

In  RODENTIA  the  shoulder  girdle  is  of  a  rather  primitive 
type.  The  scapula  is  generally  high  and  narrow,  somewhat 
as  in  Ruminantia;  it  differs,  however,  from  the  Ruminant 
scapula  in  having  a  high  acromion,  which  is  often,  as  in  the 
Hares  and  Rabbits,  terminated  by  a  long  metacromion.  The 
development  of  the  clavicle  varies,  and  sometimes  it  is  alto- 
gether absent.  It  is  frequently  connected  by  cartilaginous 
bands  or  ligaments  (fig.  104,  7  and  9),  on  the  one  hand  with 
the  scapula,  and  on  the  other  with  the  sternum.  These  un- 
ossified bands  are  remains  of  the  precoracoid.  Epicoracoidal 
vestiges  of  the  sternal  ends  of  the  coracoids  (fig.  104,  11)  are 
also  often  present. 

In  the  CARNIVORA  VERA  the  scapula  is  large,  and  generally 
has  rather  rounded  borders.  The  spine  and  acromion  are  well 
developed,  and  the  prescapular  and  postscapular  fossae  are 
nearly  equal  in  size.  The  coracoid  is  very  small,  and  the 
clavicle  is  never  completely  developed,  being  often  absent,  as 
in  the  Bears  and  most  of  their  allies.  In  the  Seals  (Phocidae) 
R.  32 


498 


THE  VERTEBRATE  SKELETON. 


the  scapula  is  elongated  and  curved  backwards,  and  has  a  very 
concave  glenoid  border.  In  the  Eared  Seals  (Otariidae)  the 
scapula  is  proportionally  much  larger  and  wider,  the  pre- 
scapular  fossa  being  specially  large,  and  being  traversed  by  a 
ridge,  which  converges  to  meet  the  spine. 


FIG.  104.     DORSAL  VIEW  OF  THE  STERNUM  AND  RIGHT  HALF  OF  THE 
SHOULDER-GIRDLE  OF  Mus  sylvaticus  x  4.     (After  PARKER.) 


1.  postscapular  fossa. 

2.  prescapular  fossa. 

3.  spine. 

4.  suprascapular  border   unossi- 

fied. 

5.  coracoid  process. 

6.  acromion. 

7.  cartilaginous  vestige   of  pre- 

coracoid  at  scapular  end  of 
clavicle. 

8.  clavicle. 

9.  cartilaginous  vestige  of  pre- 


coracoid  at   sternal  end  of 
clavicle. 

10.  omosternum. 

11.  epicoracoid. 

12.  presternum. 

13.  first  segment  of  mesosternnm. 

14.  xiphisternum. 

15.  cartilaginous   termination    of 

xiphisternum. 

16.  2nd  sternal  rib. 

17.  1st  vertebral  rib. 


SKELETON  IN  MAMMALIA.    UPPER  ARM  AND  FORE- ARM.    499 

In  the  INSECTIVORA  the  shoulder  girdle  is  well  developed 
and,  as  in  Rodents,  remains  are  met  with  of  various  parts  not 
generally  seen  in  mammals.  In  the  Shrews  the  scapula  is 
long  and  narrow,  and  has  a  well-marked  spine,  whose  end 
bifurcates,  forming  the  acromion  and  metacromion.  The 
clavicle  is  long  and  slender,  and  is  connected  with  the  sternum 
and  acromion  by  vestiges  of  the  precoracoid.  Considerable 
remains  of  the  sternal  end  of  the  coracoid  are  also  found.  In 
Potamogale,  however,  there  are  no  clavicles.  In  the  Mole  the 
shoulder  girdle  is  greatly  developed,  and  of  very  remarkable 
form.  The  scapula  is  high  and  very  narrow,  with  the  spine 
and  acromion  very  little  developed.  The  other  shoulder  girdle 
element  is  an  irregular  bone,  which  articulates  with  the 
humerus  and  presternum,  and  is  connected  by  ligaments  with 
the  scapula.  This  bone  appears  to  represent  both  the  coracoid 
and  the  clavicle,  being  formed  partly  of  cartilage  bone,  partly 
of  membrane  bone. 

In  the  CHIROPTERA  the  scapula  is  large  and  oval,  and  has 
a  moderately  high  spine  and  a  large  acromion.  The  coracoid 
process  is  well  developed  and  is  often  forked.  The  clavicles  are 
also  well  developed,  and  vestiges  of  the  precoracoid  and  of  the 
sternal  end  of  the  coracoid  are  often  found. 

In  PRIMATES  the  clavicle  and  coracoid  process  are  always 
well  developed.  In  Man  and  the  Gorilla  the  scapula  has  a 
long  straight  suprascapular  border,  a  well-developed  coracoid 
process  and  spine,  and  a  large  curved  acromion.  Vestiges  of 
the  precoracoid  occur  at  each  end  of  the  clavicle.  The  shape 
of  the  scapula  varies  much  iri  the  lower  Primates. 

THE  UPPER  ARM  AND  FORE-ARM. 

In  the  MONOTREMATA  the  humerus  is  short,  very  broad  at 
each  end  and  contracted  in  the  middle.  The  radius  and  ulna 
are  stout  and  of  nearly  equal  size,  while  the  ulna  has  a  greatly 
expanded  olecranon. 

In  the  MARSUPIALIA  the  humerus  is  generally  a  strong  bone, 

32—2 


500 


THE  VERTEBRATE  SKELETON. 


broad  at  the  distal  end  and  having  well  marked  deltoid  and 
supinator  ridges,  which  are  specially  large  in  Notoryctes.     An 


FIG.  105.     ANTERIOB  SUKFACE  OF  THE  BIGHT  HUMEKUS  OF  A  WOMBAT 


(Phascolomys  latifrons).     (After  OWEN.) 


head.  6. 

greater  tuberosity.  7. 

lesser  tuberosity.  8. 

deltoid  ridge.  9. 

ent-epicondylar    (supracondy-  10. 
lar)  foramen. 


supinator  ridge, 
external  condyle. 
internal  condyle. 
articular  surface  for  radius, 
articular  surface  for  ulna. 


ent-epicondylar  or  supracondylar  foramen  (fig.  105,  5)  is  almost 
always  present  except  in  Notoryctes.  The  radius  and  ulna  are 
always  distinct  and  well  developed,  and  a  certain  amount  of 
rotation  can  take  place  between  them.  The  ulna  of  Notoryctes 
has  an  enormous  hooked  olecranon  which  causes  the  bone  to 
be  nearly  twice  as  long  as  the  radius. 

EDENTATA.  The  Sloths  have  long  slender  arm  bones ;  the 
humerus  is  nearly  smooth  and  has  a  very  large  ent-epicondylar 
foramen  in  Choloepus,  but  not  in  Bradypus.  The  radius 


SKELETON  IN  MAMMALIA.    UPPER  ARM  AND  FORE-ARM.    501 

and  ulna  can  be  rotated  on  one  another  to  a  considerable 
extent.  The  humerus  in  all  other  Edentates  is  very  strong  and 
has  the  points  for  the  attachment  of  muscles  much  developed, 
especially  in  the  Armadillos  and  Megatheriidae.  An  ent- 
epicondylar  foramen  is  found  in  all  living  forms.  The  radius 
and  ulna  are  well  developed,  but  are  not  capable  of  much 
rotation. 

In  the  SIRENIA  the  humerus  is  well  developed  and  of  a 
normal  character.  It  is  expanded  at  each  end  and  has  a 
prominent  internal  condyle,  a  small  olecranon  fossa,  and  no 
ent-epicondylar  foramen.  In  the  Dugong  and  Rhytina  there 
is  a  bicipital  groove  and  the  tuberosities  are  distinct,  but  in 
the  Manatee  there  is  no  bicipital  groove,  and  the  tuberosi- 
ties coalesce.  The  radius  and  ulna  are  about  equally  developed 
and  ankylosed  together  at  both  ends. 

In  the  CETACEA  the  arm  bones  are  very  short  and  thick. 
The  humerus  has  a  globular  head,  and  a  distal  end  terminated 
by  two  equal  flattened  surfaces  to  which  the  radius  and  ulna 
are  united.  There  is  no  bicipital  groove,  and  the  tuber- 
osities coalesce.  The  radius  and  ulna  are  flat  expanded  bones 
fixed  parallel  to  one  another,  but  the  ulna  has  a  definite  ole- 
cranon. Scarcely  any  movement  can  take  place  between 
them  and  the  humerus,  and  in  old  animals  the  three  bones  are 
often  ankylosed  together. 

In  the  UNGULATA  VERA  the  humerus  is  stout  and  rather 
short.  The  great  tuberosity  is  always  large  and  often  overhangs 
the  bicipital  groove,  it  is  especially  large  in  Titanotherium 
(Brontops],  There  is  never  an  ent-epicondylar  foramen.  The 
radius  is  always  large  at  both  ends,  but  the  condition  of  the 
ulna  is  very  variable.  Sometimes,  as  in  Tapirus,  Rhinoceros, 
Macrauchenia,  Suina  and  Tragulina,  the  ulna  is  well  developed, 
and  quite  distinct  from  the  radius  ;  but  in  most  forms,  although 
complete,  it  is  much  reduced  distally,  and  is  fused  to  the 
radius.  Sometimes,  as  in  the  Horse  and  Giraffe,  it  is  reduced 
to  the  olecranon  and  to  a  very  slender  descending  process 


502  THE  VERTEBRATE  SKELETON. 

which  does  not  nearly  reach  the  carpus.  In  the  Tylopoda, 
though  the  ulna  is  complete  and  its  distal  end  is  often  distinct, 
it  has  coalesced  with  the  radius  throughout  its  whole  length  ; 
the  olecranon  is  generally  very  large. 

SUBUNGULATA.  In  the  large  Condylarthra  the  humerus 
has  an  ent-epicondylar  foramen,  and  the  radius  and  ulna  are 
stout  bones  nearly  equal  in  size. 

In  Procavia  the  humerus  is  rather  long,  and  has  a  very 
prominent  greater  tuberosity,  and  a  large  supratrochlear  fossa, 
but  no  ent-epicondylar  foramen. 

In  the  Proboscidea  the  humerus  is  marked  by  a  greatly 
developed  supinator  ridge,  and  is  very  long,  longer  than  the 
radius  and  ulna.  The  ulna  has  a  remarkable  development, 
having  its  distal  end  larger  than  that  of  the  radius,  it  has 
also  a  larger  articular  surface  for  the  humerus  than  has  the 
radius. 

In  RODENTIA  the  humerus  varies  much  in  its  development 
according  to  the  animal's  mode  of  life.  In  the  Hares  it  is  long 
and  straight,  with  a  small  distal  end,  and  a  slight  deltoid  ridge. 
In  the  Beaver  on  the  other  hand  the  deltoid  and  supinator 
ridges  are  considerably  developed.  There  is  generally  a  large 
supratrochlear  fossa,  but  no  ent-epicondylar  foramen. 

CARNIVORA.  In  the  Carnivora  vera  the  humerus  has  large 
tuberosities,  a  prominent  deltoid  ridge  and  a  deep  olecranon 
fossa.  The  shaft  is  generally  curved,  and  an  ent-epicondylar 
foramen  is  often  found,  though  not  in  the  Canidae,  Hyaenidae, 
and  Ursidae.  The  radius  and  ulna  are  never  united.  The 
radius  (fig.  77,  B)  has  a  very  similar  development  throughout 
its  whole  length,  while  the  ulna  has  a  large  olecranon  (fig. 
77,  C,  11)  and  a  shaft  tapering  somewhat  towards  the  distal 
end. 

In  the  Pinniped  ia  the  arm  bones  are  very  strongly  de- 
veloped. The  humerus  has  a  very  prominent  deltoid  ridge, 
and  the  proximal  end  of  the  ulna  and  distal  end  of  the 
radius  are  much  expanded. 


THE    SKELETON   IN   MAMMALIA.      THE   MANUS.        503 

In  the  INSECTIVORA  the  arm  bones  are  well  developed,  and 
the  radius  and  ulna,  though  sometimes  united,  are  generally 
distinct ;  as  a  rule  there  is  an  ent-epicondylar  foramen,  but  this 
is  absent  in  the  Hedgehog.  The  Mole  has  an  extraordinary 
humerus,  very  short  and  curved,  and  much  flattened  and  ex- 
panded at  both  ends.  It  articulates  both  with  the  scapula 
and  coraco-clavicle.  The  ulna  has  a  greatly  developed  ole- 
cranon. 

In  the  CHIROPTERA  both  humerus  and  radius  are  exceed- 
ingly long  and  slender ;  the  ulna  is  reduced  to  little  more  than 
the  proximal  end  and  is  fused  to  the  radius.  There  is  no  ent- 
epicondylar  foramen. 

All  PRIMATES  have  the  power  of  pronation  and  supination 
of  the  fore-arm,  by  the  rotation  of  the  distal  end  of  the  radius 
round  that  of  the  ulna. 

In  Man  and  the  Anthropoid  Apes  the  humerus  is  long  and 
straight,  and  has  a  globular  head ;  neither  of  the  tuberosities, 
nor  the  deltoid  nor  supinator  ridges  are  much  developed.  The 
olecranon  fossa  is  deep  and  there  is  no  ent-epicondylar  fora- 
men. The  radius  is  curved  and  has  a  narrow  proximal,  and 
expanded  distal  end,  the  ulna  is  straighter  than  the  radius 
and  has  the  distal  end  much  smaller  than  the  proximal ;  the 
olecranon  is  not  much  developed. 

In  the  lower  Primates,  although  the  radius  and  ulna  are 
always  quite  separate,  the  power  of  pronation  and  supination 
is  not  nearly  so  great  as  in  the  higher  forms.  In  most  of  the 
Cebidae  and  Lemurs  an  ent-epicondylar  foramen  occurs. 

THE  MANUS. 

The  Manus  is  divisible  into  two  parts,  viz.  the  carpus  or 
wrist,  and  the  hand  which  is  composed  of  the  metacarpals  and 
phalanges.  The  carpal  bones  are  always  modified  from  their 
primitive  arrangement,  sometimes  more,  sometimes  less.  One 
modification  however  is  always  found  in  mammals,  viz.  the 


504          THE  VERTEBRATE  SKELETON. 

union  of  carpalia,  4  and  5  to  form  the  unciform  bone.  Two 
sesamoid  bones  are  commonly  developed,  one  on  each  side  of 
the  carpus,  the  pisiform  or  one  on  the  ulnar  side  being  much 
the  larger  and  more  constant  :  it  has  been  suggested  that 
these  represent  respectively  vestiges  of  a  prepollex  and  a  post- 
minimus  digit1. 

One  or  more  of  the  five  digits  commonly  present  may  be 
lost,  and  sometimes  all  are  lost  except  the  third.  The  terminal 
or  ungual  phalanges  of  the  digits  are  commonly  specially 
modified  to  support  nails,  claws,  or  hoofs.  There  are  as  a  rule 
two  small  sesamoid  bones  developed  on  the  ventral  or  flexor 
side  of  the  metacarpo-phalangeal  articulations,  and  sometimes 
similar  bones  occur  on  the  dorsal  or  extensor  side. 

MONOTREMATA.  In  Echidna  the  carpus  is  broad,  the  sca- 
phoid and  lunar  are  united  and  there  is  no  centrale.  The 
pisiform  is  large  and  several  other  sesamoid  bones  occur.  Each 
of  the  five  digits  is  terminated  by  a  large  ungual  phalanx.  In 
OrnithorhyncTius  the  man  us  is  more  slender,  but  the  general 
arrangement  is  the  same  as  in  Echidna. 

MARSUPIALIA.  The  carpus  has  no  centrale  and  the  lunar 
is  generally  small  or  absent.  Five  digits  are  almost  always 
present.  In  Choeropus  however  the  only  two  functional  digits 
are  the  second  and  third,  which  have  very  long  closely  apposed 
metacarpals ;  the  fourth  digit  is  vestigial,  but  has  the  normal 
number  of  phalanges,  while  the  first  and  fifth  are  absent.  The 
manus  in  Notoryctes  is  extraordinarily  modified,  the  scaphoid 
and  all  the  distal  carpalia  are  apparently  fused,  the  first, 
second,  and  fifth  digits  are  very  small,  the  third  and  fourth, 
though  having  only  one  phalanx  apiece,  bear  each  an  enormous 
claw.  Lying  on  and  obscuring  the  ventral  surface  of  the  manus 
is  a  large  bone,  probably  a  sesamoid. 

Among  the  EDENTATA  there  is  a  great  diversity  in  the 
structure  of  the  manus,  the  centrale  is  however  always  want- 
ing, and  except  in  Manis  the  scaphoid  and  lunar  are  distinct. 
1  See  K.  Bardeleben,  P.  Z.  S.,  1889,  p.  259. 


THE    SKELETON    IN    MAMMALIA.      THE   MANUS.      505 

In  the  Sloths  the  manus  is  very  long,  narrow,  and  curved, 
and  terminated  by  two  or  three  long  hooked  claws,  borne 
by  the  second  and  third,  or  the  second,  third  and  fourth 
digits.  The  fifth  digit  is  absent,  and  the  fourth  is  represented 
only  by  a  small  metacarpal.  In  the  Anteaters  the  third  digit 
is  greatly  developed  and  bears  a  long  hooked  claw.  In  Myr- 
mecophaga  all  five  digits  are  fairly  well  though  irregularly 
developed,  in  Cydoturus  the  first,  fourth,  and  fifth,  are  vesti- 
gial. In  the  Armadillos  the  manus  is  broad,  and  has  strongly 
developed  ungual  phalanges.  The  digits,  though  almost  always 
five  in  number,  vary  much  in  their  relative  arrangement.  In 
Dasypus  they  are  regular,  but  are  remarkably  irregular  in 
Priodon.  The  pollex  is  absent  in  Glyptodonts  and  in  Mega- 
therium. In  Megatherium  the  fifth  digit  is  clawless  while  the 
second,  third,  and  fourth  bear  enormous  claws.  In  the  Manidae 
the  scaphoid  and  lunar  are  united;  five  digits  are  present, 
the  third  and  fourth  being  very  large,  and  all  being  terminated 
by  deeply  cleft  ungual  phalanges.  In  Orycteropus  the  pollex  is 
absent,  while  the  other  digits  are  terminated  by  pointed  un- 
gual phalanges. 

In  SIRENIA  the  general  structure  of  the  manus  is  quite  of 
the  ordinary  mammalian  type.  In  Manatus  most  of  the  bones 
of  the  carpus  are  distinct,  but  in  Halicore  many,  especially 
those  of  the  distal  row,  have  coalesced.  The  digits  are  always 
five  in  number  and  have  the  normal  number  of  flattened 
phalanges. 

In  the  CETACEA,  on  the  other  hand,  the  manus  is  much 
modified  by  the  fact  that  the  number  of  phalanges  may  be 
greatly  increased  above  the  normal  number  of  three,  thirteen 
or  fourteen  sometimes  occurring  in  each  digit.  These  are 
believed  to  be  duplicated  epiphyses.  In  the  Mystacoceti  the 
manus  remains  largely  cartilaginous,  in  the  Odontoceti  it  is 
better  ossified,  and  the  phalanges  commonly  have  epiphyses  at 
both  ends.  In  Physeter  the  carpal  bones  also  have  epiphyses. 
The  carpus  generally  consists  of  six  bones  arranged  in  two 


506          THE  VERTEBRATE  SKELETON. 

rows  of  three  each.  Five  digits  are  generally  present,  but 
sometimes  as  in  Balaenoptera  musculus,  there  are  four,  the 
third  being  suppressed.  Their  relative  development  varies 
much.  The  Sperm  Whale  which  till  recently  was  placed  in  the 
entrance  hall  of  the  Natural  History  Museum  at  South  Ken- 
sington has  one  phalanx  to  the  first  digit,  four  to  the  second, 
five  to  the  third,  four  to  the  fourth,  and  three  to  the  fifth. 
Generally  the  manus  is  short  and  broad,  but  sometimes,  as  in 
Globicephalus,  it  is  much  elongated  owing  to  the  great  develop- 
ment of  the  second  and  third  digits. 

UNGULATA1.  The  manus  of  the  members  of  this  great 
order  is  of  very  great  classificatory  and  morphological  impor- 
tance. All  the  members  agree  in  having  the  scaphoid  and 
lunar  distinct,  and  in  almost  every  case  the  ends  of  the  digits 
are  either  encased  in  hoofs  or  provided  with  broad  flat  nails. 
It  is  by  means  of  characters  derived  from  the  manus  and  pes 
that  the  group  is  subdivided  into  the  Ungulata  vera  and 
the  Subungulata. 

In  the  UNGULATA  VERA  the  manus  is  never  plantigrade, 
and  there  are  not  more  than  four  digits,  the  pollex  being  almost 
always  completely  suppressed :  in  Cotylops  among  extinct  Artio- 
dactyla  however  a  vestigial  pollex  is  found.  The  centrale  is 
absent,  and  the  magnum  articulates  freely  with  the  scaphoid, 
and  is  separated  from  the  cuneiform  by  the  unciform  and  lunar. 
A1J  the  bones  of  the  carpus  interlock  strongly,  and  the  axis  of 
the  third  digit  passes  through  the  magnum  and  between  the 
scaphoid  and  lunar. 

There  is  a  very  strong  distinction  between  the  manus  of 
the  suborders  Artiodactyla  and  Perissodactyla.  In  the  Artio- 
dactyla  the  axis  of  the  manus  passes  between  the  third  and 
fourth  digits,  which  are  almost  equally  developed  arid,  except  in 
the  Hippopotami  and  some  extinct  forms  such  as  Anoplotherium, 

1  See  E.  Cope,  "  The  origin  of  the  foot  structures  of  Ungulata,"  Journ. 
ofPhilad.  Acad.  1874.  H.  F.  Osborn,  "The  evolution  of  the  Ungulate 
foot,"  T.  Amer.  Phil.  Soc.  1889. 


THE   SKELETON   IN   MAMMALIA.      THE   MANUS.         507 

have  their  ungual  phalanges  flattened  on  their  contiguous 
surfaces. 

In  all  ARTIODACTYLA  the  third  and  fourth  digits  are  large,  but 
a  gradual  reduction  in  the  second  and  fifth  can  be  well  traced. 
Thus  in  the  Suina  the  second  and  fifth  digits,  though  smaller 
than  the  third  and  fourth,  are  well  developed  and  all  four 
metacarpals  are  distinct.  In  the  Tragulina  too  all  four  meta- 
carpals  are  developed,  and  in  Dorcatherium  the  third  and  fourth 
commonly  remain  distinct  as  in  the  Suina.  In  the  other  Artio- 
dactyla  however  the  third  and  fourth  metacarpals  are  almost 
always  united,  though  indications  of  their  separate  origin 
remain.  In  some  Ruminantia,  such  as  many  Deer,  the  second 
and  fifth  digits  are  reduced  to  minute  splint  bones  attached 
to  the  proximal  end  of  the  fused  third  and  fourth  metacarpals, 
and  to  small  hoof-bearing  phalanges,  sometimes  attached  to 
splint-like  distal  vestiges  of  the  metacarpals,  sometimes  alto- 
gether unconnected  with  any  other  skeletal  structures.  In 
some  other  Ruminants,  such  as  the  Sheep  and  Oxen,  the  only 
remnants  of  the  second  and  fifth  digits  are  nodules  of  bone 
supporting  the  hoofs,  and  in  others,  such  as  the  Giraffe,  Ano- 
plotherium  commune,  some  Antelopes  and  the  Tylopoda,  all 
traces  of  these  digits  have  disappeared.  The  Camels  differ 
from  all  living  Ungulata  vera  in  not  having  the  distal  pha- 
langes completely  encased  in  hoofs,  and  from  all  except  the 
Hippopotami  in  placing  a  considerable  amount  of  the  manus 
on  the  ground  in  walking. 

While  the  manus  of  the  Artiodactyla  is  symmetrical  about 
a  line  drawn  between  the  third  and  fourth  digits,  that  of  the 
PERISSODACTYLA  is  symmetrical  about  a  line  drawn  through  the 
middle  of  the  third  digit,  which  is  larger  than  the  others  and 
has  its  ungual  phalanx  evenly  rounded  and  symmetrical  in 
itself.  The  most  reduced  manus  in  the  whole  of  the  mam- 
malia is  found  in  the  Horse  and  its  allies,  in  which  the  third 
digit,  terminated  by  a  very  wide  ungual  phalanx,  is  the  only 
one  functional.  Small  splint  bones  representing  the  second  and 


508 


THE  VERTEBRATE  SKELETON. 


fourth  metacarpals  are  attached  to  the  upper  part  of  the  third 
metacarpal.  In  Hipparion1  and  other  early  horse-like  animals 
the  second  and  fourth  digits,  though  very  small  and  function- 
less,  are  complete  and  are  terminated  by  small  hoofs.  In  Rhi- 
noceros the  second  and  fourth  digits  are  equally  developed 
and  nearly  as  large  as  the  third,  and  reach  the  ground  in 


JT 


FIG.  106.     MANUS  OF  PERISSODACTYLES. 

A.  LEFT  MANUS  OF  Tapirus.     (After  VON  ZITTEL.) 

B.  EIGHT  MANUS  OF  Titanotherium.     (After  MARSH.) 

G.     LEFT  MANUS  OF  Chalicotherium  gigantium.     (After  GERVAIS.) 


scaphoid. 

lunar. 

cuneiform. 

trapezoid. 

magnum. 


6.  unciform. 

7.  trapezium. 

II,    III,    IV,    V.      second,   third, 
fourth  and  fifth  digits. 


walking,  a  vestige  of  the  fifth  is  also  present.     In  the  -Tapir 

1  See  0.  C.  Marsh,  various  papers  including  "Fossil  horses  in 
America,"  Amer.  Natural.  1874  ;  "  Polydactyl  horses,"  Amer.  J.  Sci.  1879 
and  1892.  M.  Pavlow,  "Le  de>eloppement  des  Equides,"  Bui.  Soc. 
Moscou,  1887,  and  subsequent  papers  in  the  same.  Osborn  and  Wortman, 
"  On  the  Perissodactyls  of  the  White  Eiver  beds,"  Bull.  Amer.  Mus.  Dec. 
23rd,  1895. 


THE    SKELETON   IN    MAMMALIA.      THE   MANUS.       509 

(fig.  106,  A)  and  Hyracotherium  the  fifth  digit  is  fully  de- 
veloped but  is  scarcely  functional.  In  Titanotherium  (Er on- 
tops]  (fig.  106,  B)  it  is  nearly  as  well  developed  as  any  of  the 
others,  and  there  is  little  or  no  difference  between  the  relative 
development  of  the  third  and  fourth  digits. 

The  Chalicotheriidae l,  though  distinctly  Perissodactyles  in 
various  respects  such  as  their  cervical  vertebrae  and  teeth, 
differ  not  only  from  all  other  Perissodactyles,  but  from  almost 
all  other  Ungulates,  in  the  very  abnormal  character  of  their 
manus.  For  while  the  carpus  and  metacarpus  are  like  those 
of  ordinary  Perissodactyles,  the  phalanges  resemble  those  of 
Edentates,  each  second  phalanx  having  a  strongly  developed 
trochlea,  and  each  distal  one  being  curved,  pointed  and  deeply 
cleft  at  its  termination  (fig.  106,  C). 

The  Macraucheniidae,  while  agreeing  with  Perissodactyles 
in  having  only  three  digits,  with  the  limb  symmetrical  about 
a  line  drawn  through  the  middle  of  the  third,  have  a  carpus 
which  approaches  closely  to  the  subungulate  condition,  the 
magnum  articulating  regularly  with  the  lunar,  and  only  to  a 
slight  extent  with  the  scaphoid. 

In  the  SUBUNGULATA  the  manus  sometimes  has  five  func- 
tional digits,  and  a  considerable  part  of  it  rests  on  the  ground 
in  walking.  The  bones  of  the  carpus  retain  their  primitive 
relation  to  one  another,  the  magnum  articulating  with  the 
lunar,  but  not  with  the  scaphoid.  This  character  does  not 
however  hold  in  the  Toxodontia,  for  in  most  of  the  animals 
belonging  to  this  group  the  magnum  does  articulate  with  the 
scaphoid.  The  corner  of  the  scaphoid  just  reaches  the  magnum 
also  in  Amblypoda. 

As  far  as  is  known  the  TOXODONTIA  generally  have  three, 
sometimes  five  digits  to  the  manus,  and  the  third  is  symme- 
trical in  itself — a  Perissodactyloid  feature. 

In  Phenacodus  (fig.  107,  B)  (CONDYLARTIIRA)  all  five  digits 

1  See  H.  F.  Osborn,  Clialicotherium  and  Macrotherium,  Amer.  Natural. 
1889—91-92. 


510 


THE  VERTEBRATE  SKELETON. 


are  well  developed,  the  pollex  being  the  smallest.     The  carpal 
bones  retain  their  primitive  arrangement,  the  magnum  articu- 


FIG.  107.  LEFT  MANUS  OF 

A.  Coryphodon  hamatus.     (After  MAKSH.)      xi. 

B.  Phenacodus  primaevus.     (After  COPE.  )      x  J . 

C.  Procavia  (Dendrohyrax)  arboreus.     (After  VON  ZITTEL.) 


1.  scaphoid. 

2.  lunar. 

3.  cuneiform. 

4.  trapezium. 

5.  trapezoid. 

6.  magnum. 


7.  unciform. 

8.  centrale. 

9.  pisiform. 

I,  II,  III,  IV,  V.  first,  second, 
third,  fourth  and  fifth 
digits  respectively. 


lating  with  the  lunar  and  not  with  the  scaphoid.  There  is  no 
separate  centrale. 

In  the  HYRACOIDEA  (fig.  107,  C)  the  manus  is  very  similar 
to  that  in  Phenacodus,  but  a  centrale  is  present  and  the  pollex 
is  much  reduced. 

The  manus  of  the  AMBLYPODA,  such  as  Coryphodon  (fig. 
107,  A)  and  Uintatherium,  is  short  and  broad,  with  five  well- 


THE   SKELETON    IN   MAMMALIA.      THE   MANUS.       511 

developed  digits  and  large  carpal  bones.  The  carpals  however 
interlock  to  a  slight  extent,  and  the  corner  of  the  magnum 
reaches  the  scaphoid. 

In  the  PROBOSCIDEA  the  manus  is  very  short  and  broad,  with 
large  somewhat  cubical  carpals  which  articulate  by  very  flat 
surfaces  and  do  not  interlock  at  all.  .All  five  digits  are  present, 
and  none  of  them  are  much  reduced  in  size.  The  manus  in 
Proboscidea  and  in  Coryphodon  is  subplantigrade. 

In  the  Tillodontia  the  manus  is  plantigrade  and  has  pointed 
ungual  phalanges,  in  this  respect  approaching  the  Carnivora. 
It  differs  however  from  that  of  all  living  Carnivora  in  having 
the  scaphoid  and  lunar  distinct. 

In  RODENTIA  the  manus  nearly  always  has  five  digits  with 
the  normal  number  of  phalanges  :  the  pollex  may  however  be 
very  small  as  in  the  Rabbit,  or  absent  as  sometimes  in  the 
Capybara.  The  scaphoid  and  lunar  are  generally  united,  and 
a  centrale  may  be  present  or  absent.  In  Pedetes  coffer  the 
radial  sesamoid  is  double  and  the  distal  bone  bears  a  nail-like 
horny  covering.  In  Bathyergus  the  pisiform  is  double.  It  is 
upon  these  facts  that  the  contention  for  the  former  existence 
of  prehallux  and  post-minimus  digits  has  partly  been  based. 

In  living  CARNIVORA  the  scaphoid,  lunar  and  centrale  are 
always  united,  forming  a  single  bone.  All  five  digits  are 
present,  but  as  a  rule  in  Carnivora  vera  the  pollex  is  small,  and  in 
Hyaena  is  represented  only  by  a  small  metacarpal.  Sometimes, 
as  in  Cats  and  Dogs,  the  manus  is  digitigrade,  sometimes,  as  in 
Bears,  plantigrade.  The  ungual  phalanges  are  large  and  point- 
ed, and  in  forms  like  the  Cats,  whose  claws  are  retractile,  they 
can  be  folded  back  into  a  deep  hollow  on  the  ulnar  side  of  the 
middle  phalanx  ;  a  small  radial  sesamoid  is  often  present. 

In  Pinniped ia  the  manus  is  large  and  flat  and  the  digits 
are  terminated  by  ungual  phalanges  which  are  blunt  (sea  lions 
and  walrus),  or  slightly  curved  and  pointed  (seals).  The  pollex 
is  nearly  or  quite  as  long  as  the  second  digit,  and  as  a  rule 
the  digits  then  successively  diminish  in  size. 


512  THE  VERTEBRATE  SKELETON. 

The  Creodonta  differ  from  living  Carnivora  in  the  fact  that 
the  scaphoid  and  lunar  are  usually  separate. 

In  INSECTIVORA  the  scaphoid  and  lunar  are  sometimes 
united,  sometimes  separate,  and  a  separate  centrale  is  usually 
present.  There  are  generally  five  digits,  but  sometimes  the 
pollex  is  absent.  In  the  Mole  the  manus  is  greatly  developed 
and  considerably  modified.  It  is  very  wide,  its  breadth  being 
increased  by  the  great  development  of  the  radial  sesamoid 
which  is  very  large  and  sickle-shaped.  The  ungual  phalanges 
are  also  large  and  are  cleft  at  their  extremities. 

In  the  CHIROPTERA  the  manus  is  greatly  modified  for  the 
purpose  of  flight.  The  pollex  is  short  and  is  armed  with  a 
rather  large  curved  claw,  the  other  digits  are  enormously 
elongated,  the  elongation  in  the  case  of  the  Insectivorous  bats 
being  mainly  due  to  the  metacarpals,  and  in  the  Frugivorous 
bats  to  the  phalanges.  In  the  Frugivorous  bats  the  second 
digit  is  clawed  as  well  as  the  pollex,  in  other  bats  this  claw  is 
always  absent,  and  so  is  often  the  ungual  phalanx,  the  middle 
phalanx  then  tapering  gradually  to  its  termination. 

In  PRIMATES  as  a  rule  the  manus  is  moderately  short  and 
wide.  The  carpus  has  the  scaphoid  and  lunar  distinct,  and 
generally  also  the  centrale :  sometimes  however,  as  in  Man, 
the  Gorilla,  Chimpanzee,  and  some  Lemurs,  the  centrale  has 
apparently  fused  with  the  scaphoid.  There  are  almost  always 
five  well-developed  digits,  but  in  the  genera  Colobus  and  A  teles 
the  pollex  is  vestigial. 

The  magnum  in  man  is  the  largest  bone  of  the  carpus.  The 
pisiform  also  is  well  developed,  but  there  is  no  radial  sesamoid. 
In  Man,  the  Gorilla,  Chimpanzee,  and  Orang,  the  carpus  arti- 
culates only  with  the  radius,  in  most  Primates  it  articulates 
also  with  the  ulna.  The  third  digit  of  the  Aye- Aye  (Chiromys) 
is  remarkable  for  its  extreme  slenderness. 

THE  PELVIC  GIRDLE. 

The  pelvic  girdle  in  all  mammals  except  the  Sirenia  and 


THE   SKELETON    IN    MAMMALIA.      PELVIC    GIRDLE.       513 

Cetacea  consists  of  two  halves,  usually  united  with  one  another 
at  the  symphysis  in  the  ID  id-ventral  line,  and  connected  near 
their  upper  ends,  with  the  sacral  vertebrae.  Each  half  forms 
one  of  the  innominate  bones,  and  includes  at  least  three  separate 
elements,  a  dorsal  bone,  the  ilium,  and  two  ventral  bones,  the 
ischium  and  pubis.  Very  often  a  fourth  pelvic  element,  the 
acetabular  or  cotyloid  bone,  occurs. 

In  the  MONOTREMATA  the  pelvis  is  short  and  broad,  and  the 
pubes  and  ischia  meet  in  a  long  symphysis.  The  acetabulum 
is  perforated  in  Echidna  as  in  birds,  but  not  in  Ornithorhynchus. 
A  pair  of  elongated  slender  bones  project  forwards  from  the 
edge  of  the  pubes  near  the  symphysis ;  these  are  sesamoid  bones 
formed  by  ossifications  in  the  tendons  of  the  external  oblique 
abdominal  muscles,  and  are  generally  called  marsupial  bones. 

In  the  MARSUPIALIA  the  ilia  are  generally  very  simple, 
straight,  and  narrow,  while  the  pubes  and  ischia  are  well  de- 
veloped and  meet  in  a  long  symphysis.  Marsupial  bones  are 
nearly  always  prominent,  but  are  not  developed  in  Thylacinus 
or  Notoryctes.  The  ischium  often  has  a  well-marked  tuberosity 
and  in  Kangaroos  the  pubis  bears  a  prominent  pectineal 
process  on  its  anterior  border  close  to  the  acetabulum.  The 
pelvis  in  Notoryctes  differs  much  from  that  in  all  other  Marsu- 
pials, the  ilium  and  ischium  being  ankylosed  with  six  vertebrae 
in  a  manner  comparable  to  that  of  many  Edentates. 

In  the  EDENTATA  the  pelvis  is  generally  well  developed,  but 
the  symphysis  is  very  short.  In  the  Sloths  the  pelvis  is  rather 
weak  and  slender,  the  obturator  foramina  are  very  large  and 
the  ischia  do  not  meet  in  a  symphysis.  In  the  Megatheriidae 
the  pelvis  is  exceedingly  wide  and  massive,  and  is  firmly 
ankylosed  with  a  number  of  vertebrae.  In  the  Armadillos, 
Glyptodonts,  Anteaters,  and  Pangolins  it  is  much  developed 
and  firmly  united  to  the  vertebral  column  by  both  the  ilia  and 
the  ischia.  In  Orycteropus  however  the  ischium  does  not 
become  united  to  the  vertebral  column,  and  the  pubis  generally 
has  a  strongly  developed  pectineal  process. 

a.  33 


514  THE  VERTEBRATE  SKELETON. 

In  the  SIRENIA  the  pelvis  is  quite  vestigial.  In  the  Dugong 
it  consists  on  each  side  of  two  slender  bones,  one  of  which 
represents  the  ilium  and  the  other  the  ischium  and  pubis  ;  the 
two  bones  are  placed  end  to  end  and  are  commonly  fused 
together.  The  ilium  is  attached  by  ligament  to  the  transverse 
process  of  one  of  the  vertebrae.  In  the  Manatee  each  half 
of  the  pelvis  is  represented  by  a  triangular  bone  connected  by 
ligaments  with  its  fellow  and  with  the  vertebral  column.  In 
neither  Manatee  nor  Dugong  is  there  any  trace  of  an  aceta- 
bulum  but  one  can  be  made  out  in  Halitherium. 

In  the  CETACBA  the  pelvis  is  even  more  vestigial  than  in 
the  Sirenia,  consisting  simply  of  a  pair  of  small  straight  bones 
which  probably  represent  the  ischia,  and  lie  parallel  to  and 
below  the  vertebral  column  at  the  point  where  the  develop- 
ment of  chevron  bones  commences. 

In  UNGULATA  VERA  the  pelvis  is  generally  rather  long  and 
narrow.  The  ilium  is  flattened  and  expanded  in  front  (fig. 
103,  8),  but  becomes  much  narrower  and  more  cylindrical 
before  reaching  the  acetabulum.  Both  pubis  and  ischium 
contribute  to  the  symphysis  which  is  often  very  long.  The 
ischia  are  large  and  have  prominent  tuberosities,  especially  in 
Artiodactyles.  In  most  Ruminantia  there  is  a  deep  depression, 
the  supra-acetabular  fossa  above  the  acetabulum,  but  this  is 
not  found  in  the  Suina  or  Tylopoda. 

SUBUNGULATA.  In  Procavia  the  pelvis  is  long  and  narrow, 
and  bears  resemblance  to  that  in  Artiodactyles. 

The  Proboscidea  have  a  very  large  pelvis  set  nearly  at 
right  angles  to  the  vertebral  column ;  the  ilium  is  very  wide, 
having  expanded  iliac1  and  gluteaP  surfaces,  and  a  narrow 
sacral1  surface.  The  pubes  and  ischia  are  rather  small,  but 
both  meet  their  fellows  in  the  symphysis.  Uintatherium  (sub- 
order Amblypoda)  also  has  a  large  and  vertically  placed  pelvis 
(fig.  108)  with  a  much  expanded  ilium.  The  pelvis  however 

1  See  p.  409. 


THE    SKELETON    IN  MAMMALIA.      PELVIC   GIRDLE.     515 

differs  from  that  of  the  Proboscidea  in  the  fact  that  the  ischia 
do  not  meet  in  a  ventral  symphysis. 

In  many  RODENTIA  the  ilia  have  their  gluteal,  iliac,  and 
sacral  surfaces  of  nearly  equal  extent ;  in  the  Hares,  however, 
the  gluteal  and  iliac  surfaces  are  confluent.  The  pubes  and 
ischia  are  always  well  developed  and  sometimes,  as  in  the 
Hares,  the  acetabular  bone  also.  In  these  animals  the  pubis 
does  riot  take  part  in  the  formation  of  the  acetabulum,  and 
the  ischium  bears  on  its  outer  side  a  well-marked  ischial 
tuberosity. 

In  the  CARNIVORA  the  pelvis  is  long  and  narrow.  The 
iliac  surfaces  (fig.  78,  A,  5)  are  very  small  and  the  sacral  large ; 
the  crest  or  supra-iliac  border  is  formed  by  the  union  of  the 
sacral  and  gluteal  surfaces.  The  symphysis  is  long  and  includes 
part  of  both  pubis  and  ischium.  The  ischial  tuberosity  (fig. 
78,  A,  10)  is  often  well  marked,  and  sometimes  as  in  Viverra 
the  acetabular  bone  is  distinct.  In  the  Pinnipedia  the  pelvic 
symphysis  is  little  developed,  or  sometimes  not  developed  at 
all,  and  the  obturator  foramina  are  remarkably  large. 

In  some  INSECTIVORA  such  as  Galeopithecus,  there  is  a  long 
pelvic  symphysis,  in  others  such  as  Erinaceus  and  Centetes,  it  is 
very  short,  in  others  again  such  as  Talpa  and  Sorex,  there  is  no 
pelvic  symphysis.  The  acetabular  bone  is  exceptionally  large 
in  Talpa  and  Sorex. 

In  CHIROPTERA.  the  pelvis  is  small  and  narrow,  and  in  the 
great  majority  of  cases  the  two  halves  do  not  meet  in  a  ventral 
symphysis.  The  pubis  has  a  strongly  developed  pectineal 
process,  which  occasionally  unites  with  a  process  from  the 
ilium  enclosing  a  large  pre-acetabular  foramen. 

PRIMATES.  In  Man  and  the  Anthropoid  Apes  the  pelvis  is 
very  large  and  wide,  and  the  ilium  has  much  expanded  iliac 
and  gluteal  surfaces.  The  symphysis  is  rather  short  and  formed 
by  the  pubis  alone.  The  acetabulum  is  deep  and  the  obturator 
foramen  large,  and  there  is  frequently  a  well-marked  ischial 
tuberosity.  In  the  lower  Anthropoidea  the  ilium  is  long  and 

33—2 


516 


THE  VERTEBRATE  SKELETON. 

1 


FIG.    108.     LEFT   ANTEBIOB  AND   POSTEBIOB   LIMB    AND   LIMB   GIBDLE  OF 
'  Uintatherium  mirabile.   The  anterior  limb  is  to  the  left,  the  posterior 
to  the  right  xTV     (From  casts,  Brit.  Mus.) 

1.  ilium.  4-     Patella. 

2.  head  of  femur.  5.     fibula. 

3.  great  trochanter.  6.     tibia. 


THE   SKELETON   IN  MAMMALIA.  THIGH   AND   SHIN.     517 

7.  second  digit  of  pes.  14.  radius. 

8.  ungual  phalanx  of  fifth  digit       15.  ulna. 

of  pes.  17.  unciform. 

9.  calcaneum.  18.  cuneiform. 

10.  postscapular  fossa.  20.  lunar. 

11.  prescapular  fossa.  21.  first  metacarpal. 

12.  coracoid  process.  22.  fifth  metacarpal. 

13.  humerus. 


narrow  and  has  a  small  iliac  surface.     The  ischial  tuberosities 
are  large  in  the  old  world  monkeys. 

THE  THIGH  AND   SHIN. 

In  the  MONOTREMATA  the  femur  is  short,  rather  narrow  in 
the  middle,  and  expanded  at  each  end.  The  great  and  lesser 
trochanters  are  large  and  about  equally  developed,  but  there  is 
no  third  trochanter.  The  fibula  is  very  large  and  is  expanded 
at  its  proximal  end,  forming  a  flattened  plate  much  resembling 
an  olecranon.  The  patella  is  well  developed. 

In  the  MARSUPIALIA  there  is  no  third  trochanter  to  the 
femur,  the  fibula  is  well  developed  but  not  the  patella  as  a 
general  rule.  Notoryctes  has  a  femur  with  a  prominent  ridge 
extending  some  little  way  down  the  shaft  from  the  great  tro- 
chanter ;  the  tibia  has  a  remarkably  developed  crest,  and  the 
fibula  has  its  proximal  end  much  expanded  and  perforated; 
there  is  an  irregularly  shaped  patella  closely  connected  with 
the  proximal  end  of  the  tibia. 

EDENTATA.  In  the  Sloths  the  leg  bones  are  all  long  and 
slender.  The  femur  has  no  third  trochanter,  and  the  fibula  is 
complete  and  nearly  equal  in  size  to  the  tibia.  In  the  Mega- 
theriidae  the  leg  bones  are  extraordinarily  massive,  the  cir- 
cumference of  the  shaft  of  the  femur  in  Megatherium  equalling 
or  exceeding  the  length  of  the  bone.  There  is  no  third  tro- 
chanter in  Megatherium.  In  most  of  the  remaining  Edentata 
the  leg  bones  are  strongly  developed.  The  femur  in  the  Arma- 
dillos and  Aard  Yarks  has  a  strong  third  trochanter,  and  the 


518 


THE  VERTEBRATE  SKELETON. 


tibia  and  fibula  are  both  large  and  are  commonly  ankylosed 
together  at  either  end.  The  limb  bones  are  very  massive  also 
in  the  Glyptodonts. 

SIRENIA.  In  no  living  Sirenian  is  there  any  trace  of  a 
hind  limb,  but  in  Halitherium  a  vestigial  femur  is  found, 
which  articulates  with  the  pelvis  by  a  definite  acetabulum. 


...4 


FIG.  109.  LEFT  FEMUR  OF  AN  Ox  (Bos  taurus)  (to  the  left)  ANI>  OF 
A  SUMATEAN  RHINOCEROS  (E.  sumatrensis)  (to  the  right),  x  ^ . 
(Camb.  Mus.) 


1.  head. 

2.  great  trochanter. 

3.  lesser  trochanter. 


third  trochanter. 

shaft. 

condyles. 


In  the  Mystacoceti  among  the  CETACEA  small  nodules  of 
bone  or  cartilage  occur  connected  with  the  vestigial  pelvis, 
and  may  represent  the  femur  and  tibia.  No  trace  of  the 
skeleton  of  the  hind  limb  is  known  in  the  Odontoceti. 


THE   SKELETON    IN    MAMMALIA.      THIGH    AND   SHIN.       519 

In  the  UNGULATA  VERA  the  femur  is  noticeable  for  the  size 
of  the  great  trochanter  (fig.  109,  2) ;  there  is  no  definitely 
constricted  neck  separating  the  head  from  the  rest  of  the 
bone,  and  the  lesser  trochanter  (fig.  109,  3)  is  not  very  promi- 
nent. All  Perissodactyles  except  the  Chalicotheriidae  show 
a  strongly  marked  third  trochanter,  but  this  is  absent  in  all 
known  Artiodactyles.  The  development  of  the  fibula  in  general 
corresponds  to  that  of  the  ulna.  In  Rhinoceros,  Jlfacrauchenia, 
Tapirus  and  the  Suina  it  is  distinct  and  fairly  well  developed  ; 
in  the  Tragulina  on  the  other  hand  it  is  vestigial,  being  reduced 
to  the  proximal  end  only.  In  the  Rumiriantia  and  Tylopoda 
also,  it  is  much  reduced  forming  merely  a  small  bone  attached 
to  the  distal  end  of  the  tibia,  sometimes  as  in  the  Red  deer 
a  slender  vestige  of  the  proximal  end  also  is  preserved  quite 
detached  from  the  distal  portion ;  in  the  Horse  this  proximal 
portion  is  all  that  there  is  found  of  the  fibula.  The  progressive 
diminution  of  the  fibula  can  be  well  seen  in  the  series  of  forms 
that  are  regarded  as  the  ancestors  of  the  Horse.  The  patella 
of  the  Ungulata  vera  is  well  ossified,  but  fabellae1  are  not 
usually  found. 

SUBUNGULATA.  Of  the  Toxodontia,  Toxodon  has  no  third 
trochanter  while  Typotherium  and  Astrapotherium  have  one. 
In  the  Condylarthra  the  femur  has  well-marked  lesser  and 
third  trochanters,  and  the  fibula  and  patella  are  well  developed. 
In  the  Hyracoidea  there  is  a  slight  ridge  on  the  femur  in  the 
place  of  the  third  trochanter,  the  fibula  is  complete,  but  is 
generally  fused  to  the  tibia  at  its  proximal  end. 

Of  the  Amblypoda,  Coryphodon  has  a  third  trochanter,  but 
Uintatherium  has  none ;  in  this  respect,  in  the  vertical  position 
and  general  appearance  (fig.  108)  of  the  limb,  and  in  the 
articulation  of  the  fibula  with  the  calcaneum,  the  leg  of 
Uintatherium  closely  approaches  that  of  the  Proboscidea. 

In  the  Proboscidea  the  femur  is  very  long  and  straight, 

1  See  p.  412. 


520  THE  VERTEBRATE  SKELETON. 

the  development  of  trochanters  is  slight,  and  the  fibula  though 
slender  is  complete  and  articulates  with  the  calcaneum. 

A  third  trochanter  is  found  in  the  Tillodontia. 

In  RODENTIA  the  femur  is  variable,  the  great  trochanter  is 
generally  large  and  so  sometimes  is  the  third  as  in  the  Hares. 
In  most  Rodents  as  in  the  Beaver  the  fibula  is  distinct,  some- 
times as  in  the  Hares  it  is  united  distally  with  the  tibia.  The 
patella  is  well  developed,  and  so  too  are  the  fabellae  as  a 
general  rule. 

GARNI VORA.  In  the  Garni vora  vera  the  femur  (fig.  79,  A) 
is  generally  rather  straight  and  slender,  and  has  a  very  distinct 
head.  The  fibula  (fig.  79,  C)  is  always  distinct  and  there  is 
generally  a  considerable  interval  between  it  and  the  tibia. 
Fabellae  (fig.  79,  7)  are  commonly  present. 

In  the  Pinnipedia  the  femur  is  short,  broad  and  flattened, 
having  a  prominent  great  trochanter.  The  fibula  is  nearly  as 
large  as  the  tibia,  and  the  two  bones  are  generally  ankylosed 
together  at  their  proximal  ends. 

The  Creodonta  differ  from  all  living  Carnivores  in  having 
a  femur  with  a  third  trochanter. 

In  the  INSECTIVORA  a  third  trochanter  is  sometimes 
developed.  The  fibula  is  sometimes  distinct,  sometimes  fused 
distally  with  the  tibia,  thus  differing  from  that  of  a  Carnivore. 

In  CHIROPTERA  the  femur  is  straight,  slender  and  rather 
short,  with  a  small  but  well-developed  head.  The  fibula  may 
be  well  developed  or  quite  vestigial  or  absent.  Owing  to  the 
connection  of  the  hind  limb  with  the  wing  membrane  the  knee 
joint  is  directed  backwards. 

In  PRIMATES  the  femur  is  rather  long  and  slender,  having 
a  nearly  spherical  head  and  large  great  trochanter.  The  tibia 
and  fibula  are  always  distinct  and  well  developed.  Fabellae 
are  not  found  in  the  highest  forms  but  are  generally  present 
in  the  others. 


THE   SKELETON   IN   MAMMALIA.      THE   PES.  521 

THE  PES. 

The  skeleton  of  the  pes  is  in  most  respects  a  counterpart 
of  that  of  the  manus.  Just  as  in  the  manus  if  one  digit  is 
absent  it  is  the  pollex,  so  in  the  pes  it  is  the  hallux.  But 
while  in  the  manus  the  third  digit  is  always  well  developed, 
however  much  the  limb  may  be  modified,  in  the  pes  any  of  the 
digits  may  be  lost.  In  all  mammals  the  tibiale  and  inter- 
medium fuse  to  form  the  astragalus,  and  the  fourth  and  fifth 
tarsalia  to  form  the  cuboid.  Sesamoid  bones  are  considerably 
developed.  In  almost  every  case  the  phalanges  and  first  meta- 
tarsal  have  epiphyses  only  on  their  proximal  ends,  while  the 
remaining  four  metatarsals  have  epiphyses  only  on  their  distal 
ends. 

In  the  MONOTREMATA  all  the  usual  tarsal  bones  are  distinct, 
and  the  five  digits  have  the  normal  number  of  phalanges. 
Several  sesamoid  bones  are  developed,  the  most  important  one, 
found  only  in  the  male,  being  articulated  to  the  tibia  and  bearing 
the  curious  horny  spur.  The  ungual  phalanges  of  the  pes  like 
those  of  the  manus,  are  deeply  cleft  at  their  extremities.  In 
the  Echidnidae  the  pes  is  turned  outwards  and  backwards  in 
walking. 

In  the  MARSUPIALIA  the  pes  is  subject  to  great  modifica- 
tions, but  in  every  case  the  seven  usual  tarsal  bones  are  dis- 
tinct. In  the  Didelphyidae  the  foot  is  broad,  all  five  digits  are 
well  developed,  and  the  hallux  is  opposable  to  the  others. 
In  the  Dasyuridae  the  foot  is  narrow,  and  the  hallux  may  be 
very  small,  or  as  in  Thylacinus  completely  absent.  In  Noto- 
ryctes  the  pes  is  much  less  abnormal  than  the  manus,  and 
all  five  digits  have  the  usual  number  of  phalanges.  The  fifth 
metatarsal  has  a  curious  projecting  process,  and  there  is  a 
large  sesamoid  above  the  hallux.  In  the  Wombats  (Phascolo- 
myidae)  the  foot  is  short  and  broad,  the  digits  are  all  distinct, 
arid  the  hallux  is  divaricated  from  the  others. 

In  the  remaining  marsupials  the  second  and  third  meta- 
carpals  and  digits  are  very  slender,  and  are  enclosed  within  a 


522          THE  VERTEBRATE  SKELETON. 

common  integument.  This  condition  is  known  as  syndactylism, 
and  its  effect  is  to  produce  the  appearance  of  one  toe  with  two 
claws.  In  the  Kangaroos  (Macropodidae)  the  pes  is  very  long 
and  narrow,  owing  to  the  elongation  of  the  metacarpals.  The 
fourth  digit  is  greatly  developed,  the  fifth  moderately  so, 
while  the  hallux  is  absent,  and  the  second  and  third  digits 
are  very  small.  The  Peramelidae  have  the  foot  constructed 
on  the  same  plan  as  in  the  Kangaroos,  and  in  one  genus 
Choeropus  the  same  type  of  foot  is  carried  to  a  greater 
extreme  than  even  in  the  Kangaroos.  Thus  the  fourth  digit 
is  enormously  developed,  the  second  and  third  are  small,  and 
the  fifth  smaller  still,  while  the  hallux  is  absent.  In  the 
Phalangers  and  Koalas  though  the  second  and  third  toes  are 
very  slender,  the  hallux  is  well  developed  and  opposable. 

EDENTATA.  In  the  Sloths  the  pes  much  resembles  the 
manus,  being  long  and  narrow,  but  in  both  genera  the  second, 
third  and  fourth  digits  are  well  developed.  Most  of  the  other 
Edentates  have  a  but  little  modified  pes  with  the  normal 
number  of  tarsal  bones  and  the  complete  series  of  digits.  In 
Cycloturus  however  the  hallux  is  vestigial  and  it  is  absent 
in  Glyptodonts.  Megatherium  has  a  greatly  modified  pes,  the 
hallux  is  absent,  and  the  second  digit  vestigial,  while  the 
third  is  very  large,  having  an  enormous  ungual  phalanx.  The 
calcaneum  too  is  abnormally  large. 

No  trace  of  the  pes  occurs  in  either  SIRENIA  or  CETACEA. 

In  the  UNGULATA  the  pes  like  the  manus  is  subject  to 
much  variation  and  is  of  great  morphological  importance. 

In  the  UNGULATA  VERA  the  pes  is  never  plantigrade  and 
never  has  more  than  four  digits,  the  hallux  being  absent. 
The  cuboid  always  articulates  with  the  astragalus,  and  the 
tarsal  bones  strongly  interlock.  As  was  the  case  also  with  the 
manus,  the  pes  is  formed  on  two  well-marked  types  character- 
istic respectively  of  the  Artiodactyla  and  Perissodactyla. 

ARTIODACTYLA.  Just  as  in  the  manus,  the  third  and 
fourth  digits  are  well  and  subequally  developed  ;  their  ungual 


THE   SKELETON    IN    MAMMALIA.       THE    PES.  523 

phalanges  have  the  contiguous  sides  flat,  and  the  axis  of  the  limb 
passes  between  them,  and  between  the  cuboid  and  navicular. 
The  astragalus  has  both  the  proximal  and  distal  surfaces 
pulley-like,  and  articulates  with  the  navicular  and  cuboid  by 
two  facets  of  nearly  equal  size.  The  calcaneum  articulates 
with  the  lower  end  of  the  fibula  if  that  bone  is  fully  developed. 

In  the  Suina  four  toes  are  developed,  and  though  in  the 
Peccaries  the  third  and  fourth  metatarsals  are  united,  they 
are  all  distinct  in  most  members  of  the  group,  as  are  all 
the  tarsal  bones.  In  the  Hippopotami  the  four  digits  are  of 
approximately  equal  size,  and  the  middle  ones  do  not  have 
the  contiguous  faces  of  their  ungual  phalanges  flattened. 

In  the  Tragulina  the  cuboid,  navicular,  and  two  outer  cunei- 
forms are  united  forming  a  single  bone  ;  all  four  metatarsals 
are  complete  and  the  two  middle  ones  are  united.  In  the 
Tylopoda  and  Anoplotherium  commune  only  the  third  and 
fourth  digits  are  developed,  their  metatarsals  are  free  distally, 
but  are  elsewhere  united.  In  the  Ruminantia  the  cuboid  and 
navicular  are  always  united  and  so  are  the  second  and  third 
cuneiforms,  while  in  Cervulus  all  four  bones  are  united 
together.  The  third  and  fourth  metatarsals  in  Ruminants 
are  always  united  in  the  same  way  as  are  the  third  and  fourth 
metacarpals,  while  the  second  and  fifth  are  always  wanting. 
In  Deer  the  second  and  fifth  digits  are  usually  each  repre- 
sented by  three  small  phalanges,  but  in  the  Giraffe  and  most 
Bovidae  the  bones  of  these  digits  are  wanting. 

In  the  PERISSODACTYLA  the  pes  like  the  manus  is  symme- 
trical about  a  line  drawn  through  the  third  digit;  this  line 
when  continued  passes  through  the  external  cuneiform,  navi- 
cular and  astragalus.  The  astragalus  has  its  distal  portion 
abruptly  truncated,  and  the  facet  by  which  it  articulates  with 
the  cuboid  is  much  smaller  than  that  by  which  it  articulates 
with  the  navicular.  The  calcaneum  does  not  articulate  with 
the  fibula.  The  tarsus  in  Macrauckenia  like  the  carpus 
differs  from  that  of  other  Perissodactyles  and  resembles  that 


524 


THE  VERTEBRATE  SKELETON. 
,1 


FIG.  110.     ^4.     LEFT  PES  OF  A  TAPIR  (Tapirus  americanus).      x£. 

.B.  RIGHT  PES  OF  A  RHINOCEROS  (E.  sumatrensis).      xf. 

C.  (CAST  OF)  BIGHT  PES  OF  Hipparion  gracile,      xf. 

D.  RIGHT  PES  OF  A  HOUSE  (Equus  caballus).     x^-.    (All  Camb.  Mus.) 

1.  calcaneum.  5.     external  cuneiform. 

2.  astragalus.  6.     middle  cuneiform. 

3.  iiavicular.  7.     internal  cuneiform. 

4.  cuboid. 


THE   SKELETON    IN   MAMMALIA.      THE   PES.  525 

of  Subungulates  in  having  the  bones  arranged  in  lines  with 
little  or  no  interlocking.  The  calcaneum  resembles  that  of 
Artiodactyles  in  having  a  small  facet  for  articulation  with  the 
fibula.  Tapirus  (fig.  110,  A),  Rhinoceros  (fig.  110,  B)  and 
Titanotherium  have  a  short  and  broad  foot  with  the  usual 
tarsal  bones  and  three  well-developed  digits, — a  number  never- 
exceeded  by  any  Perissodactyle.  From  this  tridactylate  limb 
a  series  of  stages  is  exhibited  by  various  extinct  forms  leading 
gradually  to  the  condition  met  with  in  the  Horse  (fig.  110,  D) 
in  which  the  third  toe  is  greatly  developed,  while  the  second 
and  fourth  are  reduced  to  slender  metatarsals  attached  to  the 
proximal  half  of  the  third  metatarsal. 

In  Chalicotherium  and  Agriochoerus  the  pes  has  the  same 
abnormal  characters  as  the  manus,  the  digits  being  clawed  and 
the  ungual  phalanges  in  Chalicotherium  deeply  cleft. 

In  the  SUBUNGULATA  the  pes  is  sometimes  plantigrade  and 
pentedactylate,  the  cuboid  sometimes  does  not  articulate  with 
the  astragalus,  and  the  tarsal  bones  sometimes  do  not  inter- 
lock. 

In  Typotherium  (TOXODONTIA)  the  hallux  is  absent  and  the 
other  four  digits  are  well  developed ;  in  Toxodon  and  Nesodon 
the  pes  is  tridactylate.  The  tarsal  bones  have  the  regular  Sub- 
ungulate  arrangement,  the  cuboid  not  articulating  with  the 
astragalus.  The  calcaneum  articulates  with  the  fibula  as  in 
Artiodactyles.  The  astragalus  in  most  forms,  but  not  in 
Astrapotherium,  resembles  that  of  the  Ungulata  vera  in  having 
a  grooved  proximal  surface. 

In  Phenacodus  (CONDYLARTHRA)  the  tarsus  is  very  little 
modified,  five  digits  are  present,  the  first  and  fifth  being  small 
and  not  reaching  the  ground. 

In  Procavia  only  the  three  middle  digits  are  present  with 
a  vestige  of  the  fifth  metacarpal. 

In  the  AMBLYPODA  the  pes  (fig.  108)  is  very  short  and 
broad,  all  five  digits  are  functional,  and  at  any  rate  in 
Coryphodon  plantigrade,  the  hallux  being  the  smallest.  The 


526  THE  VERTEBRATE  SKELETON. 

astragalus  is  very  flat,  and  the  tarsals  interlock  to  a  slight 
extent,  the  cuboid  articulating  with  both  calcaneum  and 
astragalus. 

The  pes  in  the  PROBOSCIDEA  much  resembles  that  in  the 
Amblypoda,  but  differs  in  that  the  astragalus  does  not  arti- 
culate with  the  cuboid,  the  tarsals  not  interlocking  at  all. 

In  the  RODENTIA  the  structure  of  the  foot  is  very  variable. 
In  Beavers  the  foot  is  very  large,  all  five  digits  being  well 
developed ;  the  fifth  metatarsal  articulates  with  the  outer  side 
of  the  fourth  metatarsal,  and  not  with  the  cuboid,  and  there 
is  a  large  sesamoid  bone  on  the  tibial  side  of  the  tarsus.  In 
the  Rats,  Porcupines  and  Squirrels,  there  are  five  digits,  in  the 
Hares  only  four,  and  in  the  Capybara  and  some  of  its  allies 
only  three.  In  the  Jerboa  (Dij)us)  a  curious  condition  of  the 
pes  is  met  with,  as  it  consists  of  three  very  long  metatarsals 
fused  together  and  bearing  three  short  toes,  each  formed  of 
three  phalanges.  Lophiomys  differs  from  all  other  Rodents 
in  having  the  hallux  opposable. 

CARNIVORA.  In  the  Carnivora  vera  the  pes  is  regular  and 
shows  little  deviation  from  the  normal  condition.  All  the 
usual  tarsal  bones  are  present,  but  sometimes  as  in  the  Dogs, 
Cats,  and  Hyaenas,  the  hallux  is  vestigial.  Sometimes  as  in 
the  Bears  the  pes  is  plantigrade,  sometimes  as  in  the  Cats  and 
Dogs  it  is  digitigrade.  In  this  respect  and  in  the  character 
of  the  ungual  phalanges,  the  pes  closely  corresponds  with 
the  manus.  In  the  Sea  Otter  (Latax)  the  foot  is  large  and 
flattened  and  approaches  in  character  that  of  the  Pinni- 
pedia. 

In  the  Pinnipedia  the  pes  differs  much  from  that  in  the 
Carnivora  vera.  In  the  Seals  in  which  the  foot  cannot  be 
used  for  walking,  and  is  habitually  directed  backwards,  the 
first  and  fifth  digits  are  much  longer  and  stouter  than  any 
of  the  others.  In  the  Sea  Lions  which  can  use  the  pes  for 
walking,  the  digits  are  all  of  nearly  the  same  length,  and 
in  the  Walrus  the  fifth  is  somewhat  the  longest. 


THE    SKELETON    IN   MAMMALIA.      THE   PES.  527 

In  the  INSECTIVORA  the  pes  is  almost  always  normal,  and 
provided  with  five  digits. 

In  the  CHIROPTERA  the  pes  is  pentedactylate,  and  the  digits 
are  terminated  by  long  curved  ungual  phalanges.  In  some 
genera  the  toes  have  only  two  phalanges.  The  calcaneum  is 
sometimes  produced  into  a  long  slender  process  which  helps 
to  support  the  membrane  between  the  leg  and  the  tail. 

Among  the  PRIMATES  Man  has  the  simplest  form  of  pes. 
In  Man  all  five  digits  are  well  developed,  the  hallux  being 
considerably  the  largest.  Sesamoid  bones  occur  only  under 
the  metatarso-phalangeal  joint  of  the  hallux. 

In  the  other  Primates  the  internal  cuneiform  has  a  saddle- 
shaped  articulating  surface  for  the  hallux,  which  is  obliquely 
directed  to  the  side  of  the  foot  and  opposable  to  the  other 
digits.  Two  sesamoid  bones  are  usually  developed  below 
each  metatarso-phalangeal  joint,  and  one  below  the  cuboid. 
The  second  digit  in  Lemurs,  and  all  except  the  hallux  in 
Ckiromys  have  pointed  ungual  phalanges ;  in  all  other  cases 
the  ungual  phalanges  are  flat.  In  some  of  the  Lemuroidea, 
especially  Tarsius,  the  tarsus  is  curiously  modified  by  the 
elongation  of  the  calcaneum  and  navicular. 


LIST   OF  AUTHORS   REFERRED   TO. 


Abbott,  E.  C.,  112 

Ameghino,  F.,  351,  424 

Andrews,  C.  W.,  299 

Balfour,  F.  M.,  16 

Ballowitz,  E.,  424 

Bardeleben,  K.,  504 

Bateson,  W.,  50,  344 

Baum,  H.,  374 

Baur,  G.,  27,  189,  190,  344,  346 

Beneden,  P.  J.  van,  353 

Benham,  W.  B.,  51 

Bettany,  G.  T.,  16.  87,  154 

Boulenger,  G.  A.,  169 

Brandt,  J.  F.,  352 

Bridge,  T.  W.,  123 

Briihl,  C.  B.,  210 

Burmeister,  H.,  351,  424, 

Cope,  E.  D.,   135,  199,  204,   351; 

359,  361,  363,  368 
Credner,  H.,  135 
Dean,  B.,  63,  104 
Dobson,  G.  E. ,  369,  370 
Earle,  C.,  432 
Ecker,  A.,  151 
Ellenberger,  W.,  374 
Flower,  W.  H.,  28,  42,  351,  420, 

422,  434 
Fritsch,  A.,  135 
Fiirbringer,  M.,  295 
Gadow,  H.,  40,  112,  190,  295,  343, 

350 

Gegenbaur,  C.,  127 
Gervais,  P. ,  353 
Giinther,  A.  C.  L.  G.,  70,  104 
Haslam,  G.,  151 
Hasse,  C.,  112,  113 
Haswell,  W.  A.,  127 

R. 


Hertwig,  0.,  169 

Hoffmann,  C.  K.,  190,  202,  210 

Howes,  G.  B.,  164,  451 

Hubrecht,  A.  A.  W.,  104 

Hulke,  J.  W.,  192,  204 

Hurst,  C.  H.,  71,  297 

Hutton,  F.  W.,  299 

Huxley,  T.  H.,  11,  13,  133, 135, 191, 

210,  295,  297,  334,  343,  351,  374, 

437 

Kirkaldy,  J.  W.,  51 
Klein,  E.,  11 
Kolliker,  A.,  9 
Ktikentbal,  W.,  349,  422       . 
Lankester,  E.  Bay,  51 
Leche,  W.,  344,  423 
Lindsay,  B.,  336 

Lydekker,  E.,  36,  42,  190,  195,  495 
Macbride,  E.  W.,  50 
Marsh,  0.  C.,  204,  209,  299,  348, 

361,  364,  365,  508 
Marshall,  A.  M.,  71,  151 
Masterman,  A.  T.,  51 
Meyer,  H.  v.,  135 
Miall,  L.  C.,  135,  243 
Mivart,  St  G.,  369 
Morgan,  C.  Lloyd,  11 
Newton,  E.  T.,  283 
Osborn,  H.  F.,  348,  420,  429,  508 
Owen,  E.,  191,  204,  210,  297,  348, 

351,  420 

Parker,  T.  J.,  83,  96,  299 
Parker,  W.  K.,  16,  24,  53,  87,  154, 

173,  200,  243,  465,  489 
Pavlow,  M.,  358,  508 
Pollard,  H.  B.,  119 
Poulton,  E.  B.,  422 

34 


530                    LIST  OF   AUTHORS   REFERRED   TO. 

Pycraft,  W.  P.,  297  Thomas,  0.,   349,  362,   370,   422, 

Ridewood,  W.  G.,  106,  164  424,  425 

Rose,  C.,  422  Tomes,  C.  S.,  420 

Sagemehl,  M.,  104  Traquair,  R.  H.,  55,  58 

Schafer,  E.,  11  Vogt,  C.,  297 

Scott,  W.  B.,  368  Wiedersheim,  R.,  25,  134,  136 

Seeley,  H.  G.,  191,  212  Wincza,  H.,  358,  495 

Selenka,  E.,  40,  295  Woodward,  A.   Smith,  34,  54,  58, 

Shufeldt,  R.,  123  62,  127,  210 

Smith,  E.  Noble,  11  Wortman,  J.  L.,  508 

Stirling,  E.  C.,  423  Wray,  R.  S.,  303 

Swirski,  G.,  103  Zittel,  K.  A.  v.,  36,  205,  212 

Taeker,  J.,  427 


INDEX. 


Every  reference  is  to  the  page :  words  in  italics  are  names  of  genera  or 
species;  figures  in  italics  indicate  that  the  reference  relates  to  syste- 
matic position ;  figures  in  thick  type  refer  to  an  illustration ;  /.  =  and 
in  following  page  or  pages;  n.  =  note. 


Aard   Vark  44,   352;   femur  517; 

sacrum    452 ;     teeth    425 ;     see 

Orycteropus 

Aard  wolf  48  ;  see  Proteles 
Abdominal    ribs,     crocodile    260 ; 

reptiles  286 

Abdominal  shield,  turtle  215 
Acanthias  32 ;  calcification  of  ver- 
tebrae 114  ;  pectoral  fins  130 
Acanthodes  32,  64 
Acanthodii  32 ;  general  characters 

64 ;  spines  106 
Acanthomys  47 ;  spines  417 
Acanthopterygii  34 
Accipitres  41 
Acetabular  bone  25,  513 ;  dog  409  f.; 

frog  165 
Acetabulum    25 ;     crocodile    266 ; 

dog  409;   duck  324;    frog  165; 

newt  149  ;  turtle  235 
Acipenser  32,  117  ;  exoskeleton  67  ; 

distribution    66 ;     pectoral    fins 

131 ;  plates  104 ;  skull  121,  122  ; 

spinal  column  112 
Acipenseridae  32 
Acrodont,   defined    199;    teeth    of 

reptiles  273 
Acrodus  32 ;  teeth  109 
Acromion,  dog  405 
Actinotrocha  30 ;  organ  regarded  as 

double  notochord  51 


Ad-digital  quill,  duck  303 
Adjutant  41  ;  clavicles  338 
^Egithognathous  335 
^Eluroidea  48,  369 ;  teeth  437 
^Epyornis  40  ;  tibio-tarsus  341 
^Epyornithes  40,  299 
Aftershaft  328 
Agama  38 ;  teeth  273 
Agamidae  38 ;  premaxillae  284 
Aglossa  36 

Agouti  48 ;  see  Dasyprocta 
Agriochoeridae  45 
Agriochoerus  45  ;  pes  525 
Ala  spuria,  duck  304 
Alcidae  42 ;  see  Auks 
Alisphenoid  19 ;  crocodile  247 ;  duck 

317 ;  dog  386 
Alligator  39,  210,  212 ;  hyoid  285  ; 

limbs  264 ;  pectoral  girdle  262  ; 

pelvis  and  sacrum  267 ;  scutes 

271 ;  skull  245,  248,  253 
Alligatoridae  39 
Alytes  36;  fronto-parietal  fontanelle 

179 ;  vertebrae  172 
Amblypoda  47  ;  general  characters 

363  ;  manus  510  ;  pes  525  ;  skull 

473 ;  teeth  433 ;  thigh  and  shin 

519 

Amblystoma  35;  skull  175 
American   monkeys   373;    see  Ce- 

bidae 

34—2 


532 


INDEX. 


American  vultures  41  ;  vomers  335 
Amia   33 ;    distribution    66 ;    exo- 

skeleton   67;  pectoral   fin   131; 

scales  105;  skull  123;  tail  115, 

117 ;  vertebrae  114 
Amiidae  33 
Ammocoetes  31,  55 
Amphibia  35 ;  anterior  limb  185 ; 

exoskeleton  168  ;  general  charac- 
ters 133 ;  hyoid  apparatus  180 ; 

pectoral  girdle  184 ;  pelvic  girdle 

187 ;    posterior   limb    188 ;    ribs 

182;    skull   173;   sternum   182; 

teeth  169 ;  vertebral  column  170 
Amphicoelous,  defined  14 
Amphioxus  30;  skeleton  51  f. ;  spinal 

column  112 
Amphisbaena  38,  272  ;  loss  of  limbs 

289 
Amphisbaenidae  38,  200;  pectoral 

girdle  288;  skull  277;  vertebral 

column  275 
Amphitheriidae  43 
Amphiuma  35, 135 ;  manus  187 ;  pes 

188 ;  skull  174 
Amphiumidae  35 
Anacanthini  33 
Anal  shield,  turtle  215 
Anas  41 ;  A.  boschas,  see  Duck 
Ankylosis,  defined  12 
Angel  fish  32 

Angler,  attachment  of  teeth  107 
Anguidae  38 
Anguilla  33;  see  Eel 
Anguis  38 ;  loss  of  limbs  289 ;  scutes 

271 
Angular   22 ;    cod   100 ;    crocodile 

258;  duck  319;  salmon  94;  turtle 

231 

Angulo-splenial,  frog  161 
Ankle  joint,  duck  327  ;  reptiles  294 
Anomodontia  36 
Anoplotheriidae  45 
Anoplotherium  45;  manus  506;  pes 

523;  tail  454;  teeth  428 
Anser  41 
Anseres  41;  aftershaft  329;  claws 

330 

Anseriformes  41 
Anteaters  352;    absence  of   teeth 

424 ;  manus  505  ;  pectoral  girdle 

495;  pelvis  513;  skull  458;  tho- 

raco -lumbar  vertebrae  447 ;  Spiny 


—  43 ;  Great  and  Two -toed  — 
44 

Antelope  359;  manus  507;  Four- 
horned  A.  46 

Anterior  limb  26  ;  Amphibia  185  ; 
birds,  338;  crocodile  263;  dog 
405 ;  duck  322 ;  frog  164  ;  newt 
147;  reptiles  290;  turtle  232 

Anthropoid  apes  373;  arm-bones 
503;  pelvis  515 

Anthropoidea  49  ;  general  charac- 
ters 372 ;  sacrum  452 ;  skull  482 ; 
teeth  441 

Anthropopithecus  49  ;  ribs  493 

Antiarcha  31  ;  general  characters  55 

Antibrachium,  see  fore-arm 

Antilocapra  46  ;  horns  417 

Antilocapridae  46 

Antitrochanter,  duck  325 

Antlers  8,  358 ;  Cervidae  469 

Antorbital  process  18 

Anura  36 ;  general  characters  136  ; 
hyoid  apparatus  180 ;  pelvis  187 ; 
posterior  limb  188;  skull  179: 
sternum  182;  vertebrae  172 

Apatornis  40  ;  vertebrae  332 

Apteria  328 

Apteryges  40 

Apteryx  40,  299 ;  aftershaft  329  ; 
anterior  nares  333  ;  claws  330 ; 
foot  342  ;  manus  338 ;  pectineal 
process  341 ;  pectoral  girdle  338 ; 
pneumaticity  of  skeleton  331 ;  A. 
owenl,  pelvic  girdle  and  sacrum 
34O 

Aqueductus  vestibuli,  dogfish  74 

Arcade:  infratemporal  — ,  crocodile 
255;  Sphcnodon  283;  inner  — , 
duck  318 ;  outer  — ,  duck  318  ; 
supratemporal  — ,  crocodile  257  ; 
reptiles  281 

Archaeoceti  44 ;  general  characters 
356  ;  skull  461 ;  teeth  426 

Archaeopteryx  40,  297  ;  claws  330  ; 
fibula  341  ;  mandible  335  ;  meta- 
tarsals  342 ;  pelvis  341  ;  ribs 
336;  sacrum  333;  skull  333; 
tail  333  ;  teeth  330 ;  wing  338 

Archaeornitb.es  40  ;  characters  297 

Archegosaurus  35,  136;  palatines 
177 

Archipterygium,  Ceratodus  127 ; 
Ichthyotomi  62 


INDEX. 


533 


Arcifera  36,  185 

Arctoidea  48,  369  ;  teeth  438 

A  rdea  41 ;  see  Heron 

Ardeae  41 

Arm,  see  fore-arm  and  upper  arm 

Armadillo  44,  352  ;  cervical  verte- 
brae 443  ;  femur  517  ;  humerus 
501 ;  lumbar  vertebrae  447  ;  ma- 
nus  505 ,  pectoral  girdle  495 ; 
pelvis  513 ;  ribs  491  ;  sacrum 
452 ;  scales  417  ;  scutes  419 ; 
skull  459  ;  teeth  424 

Armour  plates  8 

Arthrodira  34  ;  characters  70 

Articular  22 ;  cod  100  ;  crocodile 
258;  duck  319;  newt  144;  sal- 
mon 94 ;  turtle  231 

Avtiodactyla  45  ;  characters  358  ; 
manus  506 ;  odontoid  process 
445  ;  pes  522  ;  ribs  491  ;  skull 
465  ;  teeth  427  ;  thoraco-lumbar 
vertebrae  448 

Asses  360 

Asterolepis  31,  55 

Asterospondyli  114 

Astragalus  27 ;  crocodile  268 ;  dog 
414 ;  mammals  521 

Astrapotheriidae  46 

Astrapotherium  46,  361 ;  dental 
formula  432 :  femur  519 ;  pes 
525 

Ateles  49  ;  pollex  512  ;  tail  454 

Atlantosauridae  38 

Atlas  15;  crocodile  240  ;  dog  379, 
380  ;  duck  309 ;  ox  445  ;  turtle 
219 

Attachment  of  teeth  4  ;  in  fish  107 

Auchenia  45  ;  see  Llama 

Auditory  aperture  or  meatus :  ex- 
ternal —  ,  crocodile  250 ;  dog  402 ; 
turtle  228 ;  internal  — ,  crocodile 
246,  251 ;  dog  392  ;  turtle  228 

Auditory  capsule  20  ;  cod  96  ;  cro- 
codile 250  ;  dog  390  ;  dogfish  74; 
frog  156  ;  newt  143  ;  turtle  227 

Auditory  ossicles,  crocodile  251  ; 
dog  393;  duck  320;  mammals 
485  f . ;  turtle  228 

Auks  42  ;  thoracic  vertebrae  332 

Autostylic  61,  119 

Aves  40  ;  characters  295  ;  see  Birds 

Axial  skeletal  rods  50 

Axial  skeleton,  crocodile  239 ;  cod 


83 ;  dog  377 ;  dogfish  72  ;  duck 

307  ;  frog  152  ;  newt  138  ;  turtle 

218 
Axis  vertebra,  crocodile  241 ;   dog 

380 ;  duck  309  ;  turtle  220 
Axolotl  35 ',  see  Siredon 
Aye  Aye  49 ;  see  Chiromys 


Babirussa  45  ;  dental  formula  428 

Baboon  49  ;  see  Cynocephalus 

Balanoglossus  30,  50 

Balaena  44,  357;  scapula  495; 
B.  mysticetus  baleen  419 

Balaenidae  44 

Balaenoidea  44  ;  general  characters 
356 

Balaenoptera  44,  357  ;  manus  506 ; 
thoracic  vertebrae  448;  scapula 
495  ;  B.  musculus,  cervical  verte- 
brae 444 

Baleen  3,  418 

Balistes  33  ;  teeth  111 

Balistidae  33 

Ball  and  socket  joints  13 

Bandicoot  43 

Barb  302 

Barbule  303 

Barramunda  34  ;  see  Ceratodus 

Basalia,  dogfish  79 

Basi-branchial,  dogfish  78 ;  cod  101 ; 
duck  320  ;  newt  145  ;  salmon  95 

Basi-branchiostegal,  cod  101;  sal- 
mon 95 

Basicranial  axis  19  ;  dog  384 

Basidorsalia,  dogfish  72 

Basi-hyal,  dogfish  78  ;  dog  399  ; 
duck  320 

Basilar  plate  17 

Basilingual  plate,  Anura  180  ;  cro- 
codile 259  ;  frog  161 ;  turtle  231 

Basi-occipital  19  ;  crocodile  246  ; 
cod  97;  dog  386;  duck  315; 
salmon  89  ;  turtle  224 

Basipterygium,  cod  103  ;  dogfish  82 

Basisphenoid  19 ;  crocodile  247  ; 
dog  386  ;  salmon  91  ;  turtle  225 

Bastard  wing,  duck  304 

Bathyerginae,  palate  366 

Bathyergus  47  ;  auditory  ossicles 
488  ;  manus  511 

Batoidei  32,  64 

Batraclioseps  35  ;  teeth  169 


534 


INDEX. 


Bats,  claws  418  ;  Horseshoe  bats 
49  ;  see  Chiroptera 

Bdellostoma  31,  55  ;  teeth  57 

Beak  3  ;  birds  329 ;  duck  302  ; 
Siren  168 ;  tadpoles  of  Anura 
168  ;  turtle  215 

Bears  48,  369 ;  maims  511 ;  pes 
526  ;  sacral  vertebrae  452  ;  skull 
479  ;  Isabelline  —  mandible  438 

Beaver  47 ;  fibula  520  ;  humerus 
502  ;  pes  526  ;  sacrum  452 ;  tail 
454 

Belodon  39,  211;  frontals  277; 
palate  281  ;  vertebrae  275 

Bichir  33 ;  see  Polypterus 

Bicipital  groove,  dog  405 

Bilophodont,  defined  345  ;  teeth  of 
Tapiridae  429 

Bipes  38  ;  limbs  289 

Birds,  anterior  limb  338 ;  endo- 
skeleton  331f.;  exoskeleton  328f.; 
general  characters  295 ;  hyoid 
336  ;  pectoral  girdle  336 ;  pelvic 
girdle  339  ;  posterior  limb  341 ; 
ribs  336 ;  skull  333 ;  sternum  336 ; 
teeth  330  ;  vertebral  column  332 

Bison  46  ;  occipital  crest  468 

Blind  snake  38  ;  see  Typhlops 

Blind  worm  38 ;  see  Anguis 

Boidae  38 

Bombinator  36  ;  vertebrae  172 

Bone,  development  of  10  f. 

Bone  cells  10 

Bony  Ganoids,  fins  105  ;  pelvic  fin 
132  ;  ribs  126  ;  skull  123  ;  verte- 
bral column  114  ;  see  Holostei 

Border:  alveolar  — ,  of  dog's  jaw 
398 ;  coracoid,  glenoid,  and  supra- 
scapular  —  of  dog's  scapula  405 

Bos  46  ;  occipital  crest  468  ;  ribs 
491 ;  see  Ox 

Bottlenose  44  ;  see  Hyperoodon 

Bovidae  46  ;  pes  523  ;  skull  468 

Bow-fin  33  ;  see  Amia 

Brachial  ossicles,  cod  103 

Brachium  ;  see  upper  arm 

Brachydont,  defined  345  ;  teeth  of 
Ungulates  429  f. 

Brachycephalus  36  ;  bony  plates  of 
168 

Brain  case,  crocodile  245  ;  dog  384  ; 
duck  314  ;  frog  154 ;  newt  140  ; 
turtle  224 


Bradypodidae  43  ;  see  Sloths 
Brady  pus   43 ;    cervical    vertebrae 

443;  pectoral  girdle  495;    skull 

457 ;    thoraco-lumbar    vertebrae 

447 
Branchial  arches,  Amphibia  180  f .  ; 

cod  101 ;  dogfish  78  ;  fish  120  f. ; 

newt  145;  salmon  95  ;  — basket, 

Marsipobranchii  38  ;  —  skeleton, 

Amphioxus    52 ;     Balanoglossus 

50 
Branchiosaurus      35 ;        branchial 

arches  180 

Branchiostegal  rays,  cod  100 
Brontops  46  ;  see  Titanotherium 
Brontosaurus  38,  207  ;  sternum  288 
Bubalus  46 ;  ribs  491 ;  see  Buffalo 
Buccal  skeleton,  Amphioxus  52 
Buceros  42  ;  see  Hornbill 
Buckler,   of  Labyrinthodonts  168, 

184 
Buffalo  46;   Cape  — ,  skeleton  of 

492 
Bufo   36;    hyoid  182;    jaws  169; 

B.  viridis,  carpus  186 
Bufonidae  36 
Bunodont,   defined   345 ;    teeth  of 

Ungulata  427  f. 
Buno-selenodont,  defined  432 

Caeciliidae  35 

Caiman  39 ;  C.  latirostris  hyoid 
285,  limbs  264,  lateral  view  of 
skull  248,  palatal  view  of  cra- 
nium and  mandible  245,  longi- 
tudinal section  of  skull  253, 
pectoral  girdle  262,  pelvic  girdle 
and  sacrum  267  ;  C.  sclerops, 
scutes  271 

Ca'ing  whale  45 ;  see  Globicephalus 

Calamoichthys  33  ;  distribution  66 

Calamus  302 

Calcaneum  27  ;  crocodile  268 ;  dog 
414 

Calcar,  of  frog  167 

Callorhynchus  32,  66  ;  teeth  110 

Camel  45,  359 ;  manus  507  ;  teeth 
428 

Camelidae  45 

Camelus  45  ;  see  Camel 

Camptosauridae  39 

Canal:  alisphenoid — ,  dog 402;  ca- 
rotid— ,  duck  315  ;Eustachian — , 


INDEX. 


535 


crocodile  247  ;  dog  402 ;  duck 
316;  interorbital — ,  dogfish  76 

Canaliculi  10 

Canidae  48  ;  humerus  502  ;  skull 
479 ;  see  Dog 

Canine  344  ;  dog  376  f. 

Canis  48 ;  thoraco-lumbar  verte- 
brae 450 ;  see  Dog 

Capitosaurus  35  ;   skull  176 

Capybara  48;  maims  511  ;  pes  526  ; 
skull  476  ;  tail  454 

Carapace,  Chelonia  271  ;  Dcrmo- 
chelys  272 ;  Glyptodoiits  419  ; 
Green  turtle  215  ;  Loggerhead 
turtle  216 

Carcharidae  32 

Carina  sterni,  duck  321 

Carinatae  40 ;  general  characters 
300  ;  quadrate  334 

Carnassial  teeth,  368 ;  carnivora 
436  ;  dog  376  f. 

Carnivora  48 ;  arm  bones  502  ; 
auditory  ossicles  488 ;  cervical 
vertebrae  446 ;  general  characters 
367  ;  manus  511 ;  pelvis  515  ; 
pes  526 ;  ribs  493  ;  sacral  verte- 
brae 452  ;  skull  478  ;  sternum 
490;  tail  454;  teeth  437;  thigh 
and  shin  520 ;  thoraco-lumbar 
vertebrae  450 

Carnivora  vera  48 ;  general  charac- 
ters 368 ;  scapula  497 

Carp  33  ;  pharyngeal  teeth  111 

Carpo-metacarpus,  duck  324 

Carpus  26  ;  crocodile  265  ;  dog  408 ; 
duck  323  ;  frog  164 ;  newt  147  ; 
turtle  233 

Cartilage,  structure  of  10 

Cartilaginous  ganoids,  cranium 
121  ;  pelvic  fin  132 ;  spinal 
column  112  ;  see  Chondrostei 

Cassowary  40,  299  ;  aftershaft  328 ; 
bony  crest  334  ;  claAvs  330  ;  pel- 
vic girdle  and  sacrum  34 O  ; 
secondaries  329 

Castor  47  ;  see  Beaver 

Castoridae  47 

Casuarius  40  ;  see  Cassowary 

Cataphracti  34 

Cat  48,  369  ;  hallux  526  ;  manus 
511;  skull  479 

Cat-fish  33 

Cathartae  41 


Cathartes  41  ;  see  American  vulture 

Caudal  fin,  Cetacea  453  ;  fish  116  ; 

vertebrae,     crocodile     243 ; 

cod    85;    dog    383;    duck    312; 

general  characters  16;  newt  140; 

turtle  222 
Cavia  48  ;  tail  454 
Caviidae  48 
Cebidae  49,  373 ;  ribs  493  ;  skull 

484  ;  teeth  441 
Coenolestes  43,  424 
Cement  5 
Centetes  49  ;  caudal  vertebrae  454 ; 

pelvic    symphysis    515  ;    spines 

417  ;  teeth  440 ;  thoraco-lumbar 

vertebrae  450 
Centetidae  49 ;    auditory    ossicles 

488;  skull  480 

Centrale  27 ;  see  Carpus  and  Tarsus 
Centre  of  motion  448 
Centrum  14 
Cephalaspis  31,  55 
Cephalic  shield,  armadillos  419 
Cephalochordata  30,  51 
Cephalodiscus  30,  50 
Ceratodus  34,70  ;  branchial  arches 

124;     cranium    125;     skeleton 

128;    skull    117,    124;    spinal 

column  113  ;  teeth  111 
Cerato-branchial,  cod  101 ;  dogfish 

78  ;  duck  320  ;  salmon  95 
Cerato-hyal  23  ;  cod  100 ;  dog  399  ; 

dogfish  78  ;  salmon  95 
Ceratophrys  36 ;    bony    plates    of 

168  ;  teeth  170 
Ceratops  39  ;  see  Polyonax 
Ceratopsia    39 ;     characters    209 ; 

premaxillae  284 
Ceratopsidae  39 

Ceratosaurus     38,     208 ;      supra- 
temporal  fossae   283;    C.   nasi- 

cornis,  skeleton  2O6 
Cercopithecidae  49,  373 
Cervical  ribs,  crocodile   260;    rep- 
tiles 285 
Cervical  vertebrae,  crocodile  239 ; 

dog    380;    duck    307;     general 

characters   15  ;    mammals   442  ; 

turtle  219 

Cervidae  46  ;  skull  469 
Cervulus  46 ;  pes  523 
Cervus  46  ;    C.  megaceros,  antlers 

469 


536 


INDEX. 


Cestracion  32 ;  calcification  of 
vertebrae  114 ;  external  bran- 
chial arches  121 ;  pectoral  fin 
130;  skull  118;  suspensorium 
119  ;  teeth  109  ;  vertebral  column 
114 

Cestraciontidae  32 

Cetacea  44,  522 ;  arm  bones  501 ; 
auditory  ossicles  487 ;  caudal  ver- 
tebrae 453 ;  cervical  vertebrae 
444;  characters  353;  exoskeleton 
416  f. ;  hind  limb  518 ;  manus 
505  ;  pectoral  girdle  495  ;  pelvis 
514 ;  position  of  limbs  28 ;  ribs 
491 ;  skull  461  f. ;  sternum  489  ; 
teeth  426 ;  thoraco-lumbar  ver- 
tebrae 448 

Cetiosauridae  38 

Chalcides  38  ;  limbs  289 

Chalicotheriidae  46  ;  femur  519  ; 
manus  509 

Chalicotherium  46  ;  femur  360  ;  pes 
5O8,  525  ;  teeth  432 

Chamaeleon  38,  199  f.  ;  epipubis 
293  ;  ilia  291 ;  manus  291 ;  skull 
278 

Chamaeleonidae  38 

Charadriidae  42 

Charadriiformes  42 

Chauna  41 ;  interorbital  septum 
333 ;  ribs  336  ;  C.  derbiana,  spurs 
330 

Chelone37, 194  ;  plastron  271, 218 ; 
see  Turtle 

Chelonia  37',  beaks  271;  carapace 
271 ;  general  characters  193 ; 
humerus  290  ;  limbs  290  ;  palate 
281 ;  pectoral  girdle  288  ;  pelvic 
girdle  291 ;  skull  277  f.  ;  tarsus 
293  ;  vertebrae  275  f. 

Chelonidae  37 

Chelydae  37 

Chelydra  37  ;  carpus  26,  291 

Chelydridae  37 

Chelys  37,  195 

Chersidae  37 

Chevron  bones  16 ;  crocodile  243  ; 
mammals  453  f. ;  reptiles  276 

Chevrotain  45,  359  ;  teeth  429 

Chimaera  32,  66 ;  attachment  of 
fins  130  ;  pelvic  girdle  127  ;  skull 
65  ;  teeth  110 

Chimaeridae  32 


Chimaeroidei,  general  characters  65 

Chimpanzee  49  ;  carpus  512  ;  ribs 
493 ;  thoraco-lumbar  vertebrae 
450 

Chinchilla  47 ;  auditory  ossicles 
488 

Chinchillidae  47 

Chiromyidae  49 

Chiromys  49,  372 ;  manus  512  ;  pes 
527 ;  teeth  441 

Chiroptera  49 ;  auditory  ossicles 
488 ;  arm  bones  503 ;  cervical 
vertebrae  446 ;  general  characters 
370 ;  manus  512  ;  pelvis  515  ; 
pes  527  ;  sacrum  452 ;  shoulder 
girdle  499;  skull  481;  sternum 
490 ;  tail  454  ;  teeth  440  ;  thigh 
and  shin  520 ;  thoraco-lumbar 
vertebrae  450 

Chirotes  38 ;  limbs  289 

Chlamydophorus  44,  272 ;  scutes 
419 ;  skull  459 

Chlamydoselache  31 ;  branchial 
arches  121 

Choeropus  43 ;  manus  504 ;  pes 
522 

Gholoepus  43 ;  ribs  491 ;  shifting  of 
pelvis  451 ;  skull  458  ;  sternum 
489  ;  thoraco-lumbar  vertebrae 
447 ;  C.  hoffmanni  cervical  verte- 
brae 443 

Chondrocranium,  salmon  87 

Chondroid  tissue,  Balanoylossus  50 

Chondrostei  32 ;  fins  105  ;  general 
characters  67 ;  teeth  110 ;  see 
Cartilaginous  ganoids 

Chordal  sheath,  Amphioxus  52 

Chrysochloridae  49 

Chrysochloris  49  ;  auditory  ossicles 
488  ;  claws  418  ;  teeth  440 

Ciconia  41  ;  see  Stork 

Ciconiiformes  41 

Cingulum  376 

Civet  48,  369  ;  teeth  437 

Cladoselache  31,  63;  fin  129 

Clasper  132  ;  dogfish  82 

Clavicle  25;  birds  338;  cod  102; 
duck  322;  dog  405;  fish  126; 
frog  163  ;  mammals  494  f. ;  rep- 
tiles 289 

Claws  3  ;  birds  330  ;  crocodile  237 ; 
dog  374  ;  duck  302  ;  mammals 
417 ;  turtle  215 


INDEX. 


537 


Clupeidae  33 

Clupeus  33 

Cnemial  crest,  dog  412  ;  duck  326 

Coccosteus  34,  70  ' 

Coccyx,  man  454 

Cochliodontidae  31 

Cochliodus  31  ;  dental  plates  109 

Cod  33 ;  appendicular  skeleton 
101  f. ;  cranium  96 ;  mandibular 
and  hyoid  arches  99 ;  median 
fins  86 ;  pectoral  girdle  and  fin 
102;  ribs  86;  skull  96 f.;  verte- 
bral column  83  f. 

Coelofjenys  48 ;  zygomatic  arch 
477 

Coenolestes  43,  424 

Coffer-fish  33  ;  see  Ostracion 

Colobus  49  ;  pollex  512 

Colubridae  38 

Columbae  42 

Columbidae  42 

Columella,  crocodile  251 ;  duck 
320  ;  frog  157  ;  turtle  228 

Columella  cranii,  200  n. ;  see  epi- 
pterygoid 

Colymbi  40 

Colymbiformes  40 

Compsognathidae  38 

Compsognathus  38,  208 

Condylar  ridge,  duck  326 

Condyle  of  humerus,  dog  406 ;  of 
mandible,  dog  398 

Condylarthra  47 ;  femur  519 ; 
general  characters  361  ;  manus 
509  ;  skull  472  ;  teeth  432 

Contour  feather,  duck  303 

Copula  23 

Coracias  42  ;  see  Holier 

Coraciae  42 

Coraciiformes  42 

Coracoid  25  ;  cod  103 ;  crocodile 
263  ;  duck  322  ;  frog  163  ;  Mono- 
tremata  493  ;  newt  147  ;  reptiles 
288 ;  turtle  232 

Coracoid  groove,  duck  321 

Cormorant  41 ;  foot  342  ;  skull  335 

Cornu,  see  hyoid 

Cornua  trabeculae  18 

Coryphodon  47  ;  femur  519  ;  manus 
510 ;  pes  525  ;  skull  473 ;  teeth 
433  ;  G.  hamatua,  manus  51O 

Coryphodontidae  47 

Costal  plate,  turtle  215 ;  —  process, 


duck  321;  -  shield,  turtle 
214 

Cotyloid  bone,  25,  513  ;  see  Ace- 
tabular  bone 

Cotylopidae  45 

Cotylops  45 ;  pollex  506  ;  skull  468 

Coverts  306,  328 

Cranium  18 ;  cod  96  f. ;  crocodile 
244  f. ;  development  of  16  f . ;  dog 
384  f . ;  dogfish  73  f. ;  duck  314  ; 
frog  154  f.  ;  newt  140  f.  ;  turtle 
222  f. 

Cranio-facial  axis,  dog  384 

Creodonta  48 ;  carpus  512  ;  femur 
520  ;  general  characters  368 ; 
skull  479  ;  teeth  439 

Cribriform  plate,  dog  388,  400 

Crocodile  210,  212;  anterior  limb 
263;  exoskeleton  237;  pectoral 
girdle  262  ;  pelvic  girdle  266 ; 
posterior  limb  268 ;  ribs  and 
sternum  259 ;  skeleton  237  f. ; 
skull  243  f. ;  tarsus  293;  teeth 
238  ;  vacuities  in  surface  of  cra- 
nium 256  ;  vertebral  column  239 

Crocodilia  39 ;  general  characters 
of  210  ;  palate  281  ;  skull  277  f.; 
succession  of  teeth  274 ;  teeth 
273 

Crocodilidae  39 

Crocodilus  39 ;  C.  palustris,  sternum 
and  associated  bones  261 ;  late 
thoracic  and  first  sacral  verte- 
brae 242  ;  C.  vulgaris,  cervical 
vertebrae  239 

Crossopterygii  33  ;  general  charac- 
ters 68 

Crotalidae  38 

Crotalus  38 ;  jaws  280  ;  see  Rattle- 
snake 

Crows  42 

Crura  of  stapes,  dog  393 

Cruro-tarsal,  ankle  joint  345 

Crus,  26 ;  crocodile  268  ;  dog  412  ; 
duck  326;  frog  166;  neVt  149; 
turtle  235 

Crusta  petrosa  5 

Cryptobranchus  35,  135  ;  skull  175  ; 
C.  lateralis,  sacral  vertebrae  171 

Cryptodira  37  ;  characters  194 

Ctenoid  scales  8,  60,  105 

Cubitals  303  f . 

Cuboid  27  ;  dog  415 


538 


INDEX. 


Cuckoo,  foot  342 

Cuculi  42 

Cuculiformes  42 

Cuneiform  bones  27  ;  dog  414  f. 

Cyclodus  38  ;  see  Tiliqua 

Cycloid  scales  8,  60,  105  ;  cod  83 

Cyclopidhis  45  ;  skull  468 

Cyclospondyli  114 

Cyclostomata  31  ;  general  charac- 
ters 53 

Cycloturus  44  ;  hallux  522  ;  manus 
505 

Cygnus  41  ;  see  Swan 

Cynoceplialus  49 ;  cervical  vertebrae 
446 ;  skull  482 

Cynoidea  48,  369  ;  dental  formula 
437 

Cynognathus  36  ;  occipital  condyle 
277 ;  teeth  273 

Cyprinidae  33 

Cyprinus  33  ;  see  Carp 

Cypseli  42 

Cypselidae  42  ;  see  Swifts 

Cystignathidae  36 

Dactylopterus  34  ;  pectoral  fins  131 

Dasypodidae  44 

Dasyprocta  48 ;  auditory  ossicles 
488 ;  thoraco-lumbar  vertebrae 
450 

Dasyproctidae  48 

Dasypus  44 ;  manus  505 ;  skull 
459  ;  stapes  487  ;  teeth  424 

Dasyuridae  43,  350  ;  dentition  423 ; 
pes  521 ;  skull  456 

Deer  359  ;  manus  507  ;  pes  523  ; 
Chinese  water  —  46,  see  Hydro- 
potes  ;  Musk  —  46,  see  Muschus  ; 
Bed  —  fibula  519 

Delphi nidae  45 

Delphinus  45,  357  ;  lumbar  verte- 
brae 448 ;  skull  462  f . 

Deltoid  ridge,  crocodile  263  ;  dog 
406  ;  frog  164 

Dendrohyrax  363 

Dental  formula,  regular  344,  422  ; 
Anthropoidea  441 ;  Astrapothe- 
rium  432  ;  Babirussa  428  ;  Camel 
428  ;  Chiromys  441 ;  Chiroptera 
(many)  440  ;  Cynoidea  437  ; 
Dinotherium  434  ;  Dog  376  ;  Du- 
plicidentata  435  ;  Elephas  434  ; 
Erinaceus  440 ;  Felis  437 ;  Galeo- 


pithecus  440 ;  Hippopotamus  427  ; 

Horse     430;     Hydromys     436; 

Hyracoidea  362;    Macropodidae 

423  ;    Manatus   425  ;    Notary  cte* 

423;  Otorm439;  Procavia  432  ; 

Pteropus   441  ;   Kodentia   (most) 

435  ;    Kuminantia  429  ;   Squalo- 

don   427 ;     Sus   428  ;    Tapiridae 

429  ;    Thylacinus    423 ;     Uinta- 

therium  433;   Ursus  439;   Zeug- 

lodon  426 
Dentary   22 ;    crocodile   258 ;    cod 

100  ;  duck  320  ;  frog  161 ;  newt 

144  ;  salmon  94  ;  turtle  230 
Dentine  5 

Derbian  Screamer,  spurs  330 
Dermal  exoskeletou,  crocodile  237  ; 

fish  105;  mammals  419  ;  reptiles 

271  ;  turtle  215 
Dermo-supra-occipital,Labyrintho- 

dontia  177  ;  Polypterus  122 
Dermochelydidae  37 
Dermochelys    37,    194,   214,    270  ; 

carapace  and  plastron  272 
Dermoptera  48  ;  general  characters 

370 

Derotremata  35 
Desmodus  49  ;  teeth  441 
Desmognathous  319,  335 
Development     of     bone     10  ;     of 

cranium  16  ;  of  teeth  7 
Dicynodon    36,    192 ;     beak    271  ; 

supratemporal  fossa  283  ;  teeth 

273 
Didelphia  43 ;    general   characters 

349 
Didelphyidae    43,    350 ;     auditory 

ossicles  486  ;  pes  521 ;   teeth  423 
Didelphys  43 ;  atlas  443  ;  teeth  422 
Didus  42  ;  see  Dodo 
Digitigrade,  defined  358  n. 
Digits  26  ;  see  Manus  and  Pes 
Dimetrodon  36  ;  thoracic  vertebrae 

276 

Dinichthys  34,  70 
Dinocerata  364  ;  see  Uintatheriidae 
Dinornithes  40,  299  ;  see  Moas 
Dinosauria  38 ;  general  characters 

204  ;  humerus  290  ;  ischium  291 ; 

pectoral   girdle    288 ;    pes   293  ; 

pre-orbital    vacuity    284 ;     ribs 

285  ;  vertebrae  275  f. 
Dinotheriidae  47 


INDEX. 


539 


Dinotherium  47,  365  ;  dental  for- 
mula 434  ;  teeth  345 

Diodon  33 ;  beaks  111,  I),  hystrix, 
scales  105 

Diphycercal  tail  60,    116 

Diphyodont,  defined  7,  344 

Diplacanthus  32,  64 

Dipneumona  34 

Dipnoi  34  ;  general  characters  69  ; 
pelvic  fins  131 ;  skull  124  ;  spinal 
column  113  ;  tail  116  ;  teeth  111 

Dipodidae  47 

Diprotodont  423 

Diprotodontia  43  ;  characters  350 

Dipteridae  34,  70 ;  cranium  124 ; 
tail  117  ;  teeth  111 

Dipus  47 ;  cervical  vertebrae  446  ; 
pes  526 

Discoglossidae  36 

Discoglossus  36  ;  ribs  182 ;  verte- 
brae 172 

Distal,  defined  23  n. 

Divers  40 ;  thoracic  vertebrae  332 

Docidophryne  36  ;  shoulder  girdle 
and  sternum  183 

Dodo  42  ;  wing  338 

Dog  48;  arm  bones  4O7 ;  an- 
terior limb  405 ;  atlas  and  axis 
379;  cranium  384,  389,  396; 
dentition  375  ;  innominate  bone 
41O;  leg  bones  411;  manus 
408,  413,  511;  pectoral  girdle 
404;  pelvic  girdle  409;  pes,  413, 
414 ;  posterior  limb  412 ;  ribs  402 ; 
second  lumbar  vertebra  382; 
second  thoracic  vertebra  382; 
skull  383,  387;  sternum  4O3, 
404 ;  vertebral  column  378 

Dogfish  64 ;  cranium  73 ;  exoskele- 
ton  71 ;  median  tins  79  ;  pectoral 
girdle  and  fin  79;  pelvic  girdle 
81 ;  pelvic  fin  81 ;  ribs  73 ;  skull 
73,  75 ;  vertebral  column  72 ; 
visceral  skeleton  77 ;  Spotted  and 
Spiny  —  32 

Dolphin  45,  357;  lumbar  vertebrae 
448;  Gangetic  —  45,  see  Pla- 
tanista 

Donkey,  skull  431 

Dorcaiherium  45 ;  manus  507 

Dorsal  vertebra  16 

Dorsal  shield,  crocodile  238 

Down  feathers  306 


Draco  38;  ribs  286 
Dromaeognathous  335 
Dromaeus  40,  299;  see  Emeu 
Duck  41,  334;    beak    329;    claws 
330;  cranium  313;  exoskeleton 
302;  pectoral  girdle  321;  pelvic 
girdle  324,  311,  325;  pes,  327; 
posterior    limb    326;    ribs   320; 
skull  312,  312,   313;    sternum 

321,  vertebral  column  307 ;  wing 

322,  304,  305 

Duckbill  43;  see  Ornithorhynchus 
Dugong  44 ;  humerus  501 ;   pelvi 

514;    thoraco-lumbar    vertebrae 

448 ;  see  Halicore 
Duplicidentata    48,    366;     dental 

formula  435 ;  skull  478 

Eagles  335 

Eared  Seals  369;  scapula  498;  see 
Otariidae 

Echidna  43;  caudal  vertebrae  453; 
manus  504;  pelvis  513;  sacral 
vertebrae  451;  shoulder-girdle  and 
sternum  494  ;  skull  455 ;  spines 
417  ;  spur  418 ;  thoraco-lumbar 
vertebrae  447 

Echidnidae  43;  pes  521 

Ectethmoid  21  n. 

Ectocondylar  ridge,  dog  406 

Edentata  43 ;  auditory  ossicles  487 ; 
arm  bones  500;  caudal  vertebrae 
453 ;  cervical  vertebrae  443  ;  ma- 
nus 504 ;  pectoral  girdle  495 ;  pes 
522;  pelvis  513;  ribs  491;  sa- 
crum 452;  skull  457;  sternum 
489;  teeth  424;  thigh  and  shin 
517;  thoraco-lumbar  vertebrae 
447 

Eel  33 ;  scales  105 

Elasmobranchii  31 ;  cranium  118  f. ; 
clasper  132 ;  general  characters 
61;  pelvic  fins  131;  ribs  125; 
teeth  109;  vertebral  column  113  f. ; 
visceral  arches  120 

Elasnwtherium  46 ',  mesethmoid  470 

Elephant  47 ;  auditory  ossicles  487; 
caudal  vertebrae  453 ;  ribs  491 ; 
skull  473 f.,  474  and  475  ;  tusks 
420  ;  see  also  Proboscidea 

Elephantidae  47 

Elephas47, 364;  dental  formula  434; 
E.  plantfron*  435 ;  see  Elephant 


540 


INDEX. 


Elginia  36;  skull  191,  283 

Embolomerous  172 

Emeu  40,  299;  aftershaft  328; 
claws  330 

Enamel  4 ;  —  cap  7  ;  —  organ  7 

Endochondral  ossification  11 

Endoskeleton,  Amphibia  170;  birds 
331  f. ;  cod  83  f. ;  crocodile  239  f. ; 
dog  377  f. ;  dogfish  71  f .  ;  duck 
306  f.;  fish  112f.  ;  frog  151  f.; 
mammals  442  f. ;  newt  138  f. ; 
reptiles  275  f. ;  turtle  218  f . 

Engystomatidae  36 

Entoplastron,  turtle  217 

Epanorthidae  43,  350 

Epi-branchial,  cod  101 ;  dogfish  78 ; 
salmon  94 

Epicoracoid  25 ;  frog  163 ;  turtle 
232  ;  Monotremes  493  ;  vestiges 
of  in  Kodentia  497 

Epicrium  35 ;  orbit  179 

Epidermal  exoskeleton,  birds  328; 
crocodile  237;  dog  374;  duck 
302  ;  mammals  416 ;  reptiles 
270;  turtle  214 

Epi-hyal,  cod  100 ;  dog  399;  salmon 
94 

Epi-otic  20 ;  cod  96 ;  crocodile  250 ; 
Labyrinthodontia  177;  reptiles 
278 ;  salmon  89 ;  turtle  227 

Epiphysis  11 

Epiplastron,  turtle  217 

Epiprecoracoid,  Amphibia  184 ; 
turtle  232 

Epipterygoid,  Lacertilia  200;  rep- 
tiles 278 

Epipubis,  crocodile  267 ;  newt  149 ; 
turtle  235 

Episternum  217;  frog  163 

Equidae  46;  mane  416;  scapula 
496;  skull  471 

Equus  46;  see  Horse 

Erinaceidae  49 

Erinaceus  49 ;  dental  formula  440 ; 
pelvic  symphysis  515;  prester- 
num  490 ;  see  Hedgehog 

Esocidae  33 

Esox  33;  attachment  of  teeth  107 

Ethmoid  394 ;  see  median  ethmoid 

Ethmoidal  plane  390 ;  —  region  21 

Ethmo-palatine  ligament,  dog- 
fish 77 

Ethmo-turbinal,  dog  395 


Euchirosaurus  35;  vertebrae  171 
Eustachian  canal;  see  Canal 
Eusuchia  39;    general   characters 

212 

Eutheria  43;  general  characters  351 
Exocaetus  33;  pectoral  fins  131 
Exoccipital  19;   cod  97;  crocodile 
246;    dog  386;    duck  314;    frog 
154;     newt     141;     salmon    89; 
turtle  224 

Exoskeleton  2 ;  Amphibia  168 ;  birds 
328;    crocodile    237;    dog    374; 
dogfish  71;  duck  302;  fish  104; 
ganoids  66 ;  mammals  442 ;  rep- 
tiles 270 ;  turtle  214 
Extensor  side,  defined  29 
Extra-branchial,  dogfish  79 
Extra-columella,     crocodile     251 ; 
turtle  228 

Fabella,  dog  412 

Falco  41 

Falcon  41,  335 

Falconiformes  41 

Feathers  3,  328;  duck  302 

Felidae  48 ;  claws  418 

Felis  48;  dental  formula  437;  tho- 

raco-lumbar  vertebrae  450 
Femoral  shield,  turtle  215 
Femur  26;  crocodile  2€8;  dog  412; 

duck  326;   frog  166;  mammals 

517 f.;  newt  149;  ox  and  rhino- 
ceros 518;  turtle  235 
Fenestra    ovalis,   crocodile   250  f. ; 

dog   392;    duck   316;    frog  157; 

turtle  228  ;  —  rotunda,  dog  392; 

duck  316 

Fenestral  recess,  duck  316 
Fibula  26 ;  crocodile  268 ;  dog  412 ; 

duck  327;  frog  166;   newt  149; 

turtle  235 

Fibulare  27 ;  see  Tarsus 
File-fish  33 ;  see  Batistes 
Filoplume  306 
Finches  42 
Fins,  fish  115;  caudal — ,  Cetacea 

453;  cod  87;  fish  116;   Ichthyo- 

sauria  195;  median  — ,  cod  86; 

dogfish  79;  pectoral  — ,  cod  103; 

dogfish  79;  pelvic  — ,  cod  103; 

dogfish  81 
Fin-rays   105,  115;    cod  83,    103; 

dogfish  79 


INDEX. 


541 


Firmisternia  36,  185 

Fish,  appendicular  skeleton  126; 
endoskeleton  112  f.  ;  exoskeleton 
104;  general  characters  60  f. ; 
paired  fins  127  f. ;  ribs  125  f. ; 
skull  117  f. ;  spinal  column  112  f. ; 
teeth  106  f. 

Fissipedia  48',  general  characters 
368 

Flamingo  335 

Flexor  side,  defined  29 

Floating  ribs,  dog  402;  mammals 
490 

Flower,  Sir  W.  H.,  on  succession  of 
teeth  in  elephants  434 

Flying-fish  33;  —  fox  49,  371,  skull 
481,  see  Ptcropux  ;  —  gurnard  34, 
see  Dactyloptvrus;  —  lemur  48, 
see  Galeopithecus;  —  lizard  38, 
see  Draco 

Fontaiielle,  salmon  89 ;  anterior  — , 
dogfish  74 ;  frog  154 ;  posterior  — , 
frog  154 

Foot,  crocodile  269 ;  dog  414 ;  frog 
167 ;  newt  149  f. ;  turtle  236 

Foramen :  anterior  palatine  — ,  dog 
401 ;  condylar — ,  dog  401 ;  — cor- 
diforme,  reptiles  292;  ect-epicon- 
dylar  — ,  Sphenodon  290 ;  ent-epi- 
coudylar  —  191  n. ;  Carnivora 
vera  502;  Cebidae  503;  Choloe- 
pus  500;  Condylarthra  362,  502; 
Creodonta  368 ;  Insectivora  503 ; 
Lemurs  503 ;  Marsupials  500 ; 
reptiles  290 ;  external  mandibular 
— ,  crocodile  258 ;  inferior  dental 
— ,  dog  399 ;  infra-orbital  — ,  dog 
401;  Kodents  477 ;  ilio-sciatic  — , 
duck  325 ;  internal  mandibular 
— ,  crocodile  258 ;  internal  orbital 
— ,  dog  401;  interparietal  — , 
Labyrinthodontia  173,  177;  rep- 
tiles 277;  —  lacerum  anterius, 
dog  388,  400;  —  lacerum  me- 
dium, dog  402;  —  lacerum  pos- 
terius,  dog  392,  401;  lachrymal 
— ,  dog  394,  401;  —  magnum, 
cod  97;  crocodile  257;  dog  386, 
402;  dogfish  76;  duck  314;  frog 
154;  newt  141;  salmon  89; 
turtle  224;  mental — ,  dog  399; 
obturator  — ,  duck  326;  dog  410; 
ophthalmic  — ,  dogfish  74;  optic 


— ,  dog  400 ;  dogfish  74  ;  orbi- 
tonasal  — ,  dogfish  74;  —  ovale, 
crocodile  249;  dog  400;  pneu- 
matic — ,  duck  323;  pneumo- 
gastric  — ,  dogfish  76;  posterior 
palatine  — ,  dog  401 ;  post-  glenoid 
— ,  dog  402;  pre-acetabular  — , 
Chiroptera  515;  —  rotundum, 
dog  400;  stylomastoid  — ,  dog 
392  f.,  400;  thyroid  — ,  dog  410; 
trigeminal  — ,  duck  316 ;  —  tri- 
osseum,  duck  322 

Fore-arm  26;  crocodile  265;  dog 
406;  duck  323;  frog  164;  newt 
147 ;  turtle  233 

Fossa :  cerebellar  — ,  dog  392 ;  cere- 
bral — ,  dog  392  ;  digital  — ,  dog 
412  ;  floccular  — ,  dog  392 ;  infra- 
temporal  — ,  see  lateral  temporal 
— ,  lachrymal  — ,  Kuminants 
469;  lateral  temporal  — ,  croco- 
dile 257 ;  Sphenodon  283  ;  ole- 
cranon  — ,  dog  406;  prescapular 
— ,  dog  405 ;  postscapular  — ,  dog 
405;  post-temporal  — ,  Spheno- 
don 283;  pterygoid  — ,  crocodile 
257;  suborbital  — ,  Kuminants 
469;  supra-acetabular  — ,  Kumi- 
nants 514;  supra-temporal  — , 
crocodile  249,  256;  reptiles  283; 
supra-trochlear  — ,  dog  406 ;  tem- 
poral — ,  dog  398;  trochanteric 
— ,  dog  412 

Fowl  41,  335;  claws  330;  skeleton 
301 

Fox  48 

Frigate  bird  41 ;  clavicles  338 

Frog,  anterior  limb  164;  cranium 
155,  157  ;  hyoid  apparatus  161 ; 
pelvic  girdle  165 ;  posterior  limb 
166;  shoulder  -  girdle  and  ster- 
num 183;  skull  154  f.,  155, 
159;  teeth  151;  vertebral  co- 
lumn 152;  Common  — ,  Edible 
— ,  Fire-bellied  — ,  Green-tree 
— ,  Horned  — ,  Midwife  — , 
Painted  —  and  Toad  —  36 

Frontal  19;  cod  96;  crocodile  249; 
dog  388;  duck  314;  newt  141; 
salmon  91;  turtle  225;  —  seg- 
ment, crocodile  249;  dog  388; 
turtle  225 

Fronto-parietal,  frog  156 


542 


INDEX. 


Frugivorous  bats,  manus  512 ;  see 

Pteropidae 

Fulcra  67;  Polypterus  106 
Furcula296;  duck  322 

Gadidae  33 

Gadus  33 ;  see  Cod 

Galeopithecidae  48 

Galeopithecus  48,  370;  dental  for- 
mula 440 ;  iutercentra  450 ;  pel- 
vic sympliysis  515 ;  skull  480 

Galesaurus  36,  192 ;  teeth  273 

Galeus,  32;  occipital  joint  118 

Clalli  41 

Gallif  ormes  41 

Gallus  41 ;  G.  bankiva  skeleton  3O1 

Gannet,  41 ;  wing  339 

Ganoid  scales  8,  60,  104 

Ganoidei  32;  general  characters 
and  distribution  66;  pectoral 
girdle  126 ;  pelvic  fins  132 ;  teeth 
110;  skull  121  f. ;  spinal  column 
112  and  114 

Garialidae  39 

Garialis  39,  212 

Garial  210 

Gar  pike  33 ;  see  Lepidosteus 

Gavialis  39 

Gazella  46 

Gazelle4<S;  skull  468 

Geckonidae  37 ;  see  Gecko 

Gecko  37;  epipubis  293;  parietals 
277;  supra-temporal  fossa  283; 
vertebrae  275 

Gibbon  49;  ribs  493;  skull  482 

Gill-rays,  dogfish  78 ;  salmon  95 

Giraffa  46 

Giraffe  46,  359;  cervical  vertebrae 
445 ;  manus  507 ;  pes  523 ;  ulna 
501 

Giraffidae  46 ;  skull  469 

Girdle  bone,  frog  156 

Glenoid  cavity  25;  crocodile  263; 
dog  405;  duck  322;  frog  162; 
newt  146;  turtle  232;  —  fossa, 
dog  394 

Globe-fish  33 

GloNcephalus  45;  cervical  vertebrae 
354  ;  manus  506  ;  skull  463 

Gluteal  surface  of  ilium,  dog  410 

Glyptodon  44;  carapace  419;  cervi- 
cal vertebrae  443 ;  caudal  verte- 
brae 453 ;  mauus  505  ;  pelvis  513 ; 


pes    522;    teeth    425;    thoraco- 

lumbar  vertebrae  447 
Glyptodontidae  44,  352 ;  skull  459  ; 

see  also  Glyptodon 
Gnathostomata  31,  59 
Golden  mole  49 ;  see  CJirysochloris 
Goniopholidae  39 
Goniopholis  39  ;  vertebrae  275 
Goose  334  ;  beak  329  ;  Spur-winged 

—  41 
Gorilla  49 ;  carpus  512 ;  ribs  493  ; 

scapula  499;  skull  483;  thoraco- 

lurnbar  vertebrae  450 
Gruidae  41 ;  see  Cranes 
Gruiformes  41 
Guinea-pig  48;  tail  454 
Gular  shield,  turtle  215 
Gulls  42,  335 ;  aftershaft  328 
Gymnodontidae  55;  beaks  111 
Gymnophiona  35 ;  branchial  arches 

180 ;  general  characters  136 ;  ribs 

182;  scales  168;  skull  177;  teeth 

169 ;  vertebrae  172 
Gymnura  49 ;  teeth  440 ;  zygomatic 

arch  481 

Gypogeranus  41 ;  claws  330 
Gyrinophilus  35;  vertebral  column 

171 

Haddock  55 

Hadrosauridae  39 

Hadrosaurus  39 ;  skull  284 

Hag  or  hag-fish  31,  54  f. 

Hair  3 ;  dog  374 ;  mammals  416 

Halicore  44,  352 ;  manus  505 ;  skull 

460 ;  teeth  425 ;  see  Dugong 
Halicoridae  44 
Halitheriidae  44 
Halitherium  44,  352  ;    femur  518  ; 

pelvis  514 ;  teeth  425 
Hallux   26;    dog   415;   duck  327; 

frog  167 

Hamular  process,  dog  397 
Hand,  crocodile  266;   dog  408  f.; 

duck  324;  frog  165;  newt  147; 

turtle  233 
Hapale  49 

Hapalidae  49,  372  f. ;  teeth  441 
Hare    48,    366 ;    acetabular    bone 

515  ;  dental  formula  435  ;  femur 

520 ;  humerus  502 ;   pelvis  515  ; 

scapula    497;     skull    476;     tail 

454 ;     thoraco-lumbar    vertebrae 


INDEX. 


543 


449;  Cape  jumping  —  47',  see 
Pedetea 

H(irp<t(/ux  41 ;  serrated  beak  334 

Harriotta  32,  66 

Hatter ia  37,  197;  see  Sphenodon 

Haversian  canals  10;  —  system 
10 

Hawks,  beak  of  330 

Hedgehog  49, 370 ;  auditory  ossicles 
488 ;  humerus  503  ;  presteriium 
490 ;  skull  480 ;  spines  417  ;  see 
Erinaceut 

Hemichordata  30,  50 

Hi'ptanchiis  31 ;  branchial  arches 
63,  120;  vertebrae  114 

Herbivorous  dentition  427,  430 

Heron  41,  335;  inter-orbital  sep- 
tum 333  ;  powder  down  feathers 
329 

Herring  33 

Hesperornis  40,  299 ;  caudal  ver- 
tebrae 333  ;  clavicles  338  ;  teeth 
330  ;  wing  338 

Heterocercal  tail  60,  116 

Heterodont  7 

Heterostraci  31 ;  general  character 
54 

Hexanchus  31 ;  branchial  arches 
63,  121 

Hinge  joint  13 

Hipparion  46 ;  manus  508 ;  pes 
524 

Hippopotamidae  45 

Hippopotamus  45,  359;  dental  for- 
mula 427 ;  hair  416 ;  mandible 
467;  manus  506;  pes  523;  sca- 
pula 496 ;  skull  467  ;  teeth  345 

Hoatzin  41 ;  see  Opisthocomus 

Holocephali  32,  65,  104;  clasper 
132;  spinal  column  113;  tail  116; 
teeth  109 

Holoptychiidae  33 

Holopty chins  33  ;  scales  105 

Holostei  33;  general  characters  68  ; 
teeth  110  ;  see  Bony  Ganoids 

Hominidae  49,  373 

Homo  49 ;  see  Man 

Homocercal  tail  60,  69, 117;  codfish 
87 

Homodont,  defined  7 

Hoofs  3 ;  418 

Hoopoe  42,  335 

Hoplopterus,  spur  330 


Hornbill  42,  331 ;  bony  crest  334  ; 
interorbital  septum  333 

Horns  3,  417 

Horny  plates   on   palate   418;    - 
teeth,  Lampreys  4;    Myxinoids 
57 ;  Ornithorhynchm  4 

Horse  46,  360 ;  fibula  519  ;  malleus 
487  ;  manus  507  ;  pes  524  ;  skull 
471 ;  teeth  345,  430  ;  ulna  501 

Howling  monkey  49 ;  see  Mycetes 

Humerals,  duck  303  f. 

Humeral  shield,  turtle  215 

Humerus  26 ;  crocodile  263 ;  dog 
405;  duck  323;  frog  164;  newt 
147 ;  turtle  232  ;  wombat  5OO 

Humming-birds  42,  335 

Humpbacked  whale  44,  357 

Hyaena  48,  369 ;  hallux  526 ;  pol- 
lex  511;  sacral  vertebrae  452; 
teeth  437 

Hyaenidae  48;  humerus  502 

Hyaenodon  48,  368 

Hyaenodontidae  48 

Hyaline  cartilage  10 

Hydrochaerus  48 ;  teeth  437 ;  see 
Capybara 

Hydromys  47 ;  dental  formula  436 

Hydrophidae  38 ;  scales  270 

Hydropotes  46 ;  canines  429 

Hyla  36;  fronto-parietal  fontanelle 
179 ;  sternum  184 

Hylidae  36 

Hylobates  49 ;  ribs  493  ;  skull  482 

Hyoid  21 ;  alligator  285 ;  Amphibia 
180  ;  birds  336  ;  cod  100  ;  croco- 
dile 259;  dogfish  77;  dog  399; 
duck  320;  frog  161;  newt  144; 
reptiles  284;  salmon  94;  turtle 
231,  285 

Hyomandibular  23 ;  cod  100  ;  dog- 
fish 78 ;  salmon  94 

Hyomoschus  45 

Hyoplastron,  turtle  217 

Hyostylic  61,  119 

Hyotherium  45;  teeth  427 

Hyperodapedon  37, 198 ;  premaxillae 
284 

Hyperoodon  44 ;  skull  464 ;  sternum 
489  ;  thoracic  vertebrae  448 

Hypo-branchial,  cod  101;  dogfish 
78 

Hypo-hyal,  cod  100  ;  salmon  95 

Hypo-ischium,  Lacertilia  292 


544 


INDEX. 


Hypoplastron,  turtle  217 

Hyporachis  328 

Hypsilophodon  39 ;  predentary  bone 
284 

Hypsodont,  defined  345,  429 

Hypural  bone,  cod  85 

Hyracidae  47 

Hyracoidea  47 ;  femur  519 ;  general 
characters  362 ;  manus  510  ;  nails 
418  ;  skull  472 ;  teeth  432 

Hyracotherium  46;  manus  508; 
scapula  496 

Hyrax  47,  363;  see  Procavia 

Hystricidae  47 

Hystricomorpha  47;  auditory  os- 
sicles 488 

Hystrix,  47 ';  auditory  ossicles  488; 
see  Porcupine 

Ichthyodorulites  106 

Ichthyoidea  35 ;  general  characters 

134 
Ichthyopsida3jf ;  general  characters 

59 

Ichthyopterygium  130 
Ichthyornis    40 ;     mandible    335 ; 

pelvis  341 ;  teeth  330  ;  vertebrae 

332 

Ichthyornithiformes  40,  300 
Ichthyosauria  37;  general  charac- 
ters 195 ;  ribs  285 
Ichthyosauridae  37 
Ichthyosaurus  37,197;  limbs  290; 

palatines    281 ;    pectoral    girdle 

288 ;  position  of  limbs  28 ;  skull 

196 ;  teeth  273 ;  vertebral  column 

275 
Ichthyotomi  31 ;  general  characters 

62;  fins  1 30  f.;  tail  116 
Iguana  38 ;  teeth  273 
Iguanidae  38;    zygosphenes    200, 

276 
Iguanodon  39,   208  f.;   jaws   292; 

predeutary   284 ;    sternum   288  ; 

teeth  272  f. ;  vertebrae  275 
Iguanodontidae  39 
Iliac  surface  of  ilium,  dog  410 
Ilium  25 ;  crocodile  266  ;  dog  409  ; 

duck  325;  frog  165;   mammals 

513  f. ;  newt  149 ;  reptiles  291 ; 

turtle  235 
Incisors,    dog    376   f.  ;    mammals 

344 


Incus,  dog  393;  man,  dog  and 
rabbit  485 

Infra-marginal  shield,  turtle  215 

Infra-pharyngeal  bone,  cod  101 

Inia  45 ;  cervical  vertebrae  444 ; 
lumbar  vertebrae  448 

Innominate  bone,  dog  409 ;  mam- 
mals 513 

Insectivora  48 ;  arm  bones  503 ; 
auditory  ossicles  488 ;  cervical 
vertebrae  446 ;  general  characters 
369  f. ;  manus  512  ;  pelvis  515; 
pes  527 ;  sacrum  452 ;  shoulder- 
girdle  499;  skull  480;  sternum 
490;  tail  454;  teeth  440;  thigh 
and  shin  520 ;  thoraco-lumbar 
vertebrae  450 

Insectivora  vera  49;  general  cha- 
racters 370 

Intercentra  15  ;  Galeopithecus  370 ; 
Ichthyosauria  195;  Labyrintho- 
dontia  172 ;  Sphenodon  198 ; 
Talpa  450 

Interclavicle  25 ;  crocodile  263 ; 
Monotremata  494  ;  reptiles  289 

Intercondylar  notch,  dog  412 

Intergular  shield,  turtle  215 

Interhyal,  cod  100 

Intermedium  27;  see  Carpus  and 
Tarsus 

Intermuscular  bones,  cod  86 

Internasal  septum,  dogfish  76 

Interorbital  septum,  birds  333 ; 
crocodile  247  ;  duck  317 ;  reptiles 
277 

Interspinous  bones,  cod  86 

Intertarsal  ankle  joint  190 

Intervertebral  discs  15,  378 

Ischial  tuberosity,  dog  411 

Ischium  25 ;  crocodile  266 ;  dog 
410 ;  duck  325  ;  frog  165 ;  newt 
149 ;  turtle  235 

Ischyodus  32,  66 

Ivory  5 

Jacana  42 ;  see  Parra 
Jacare  39;  scutes  271 
Jaws  21 ;  cod  98  f. ;  crocodile  252  f.; 

dog  395f . ;  dogfish  77 ;  duck  317  f .; 

frog  158  f. ;  newt  143  f. ;  salmon 

93  f . ;  turtle  229  f. 
Jerboa  47;  cervical  vertebrae  446; 

pes  526 


INDEX. 


545 


Joints,  kinds  of  13 

Jugal  22 ;  crocodile  255  ;  dog  398  ; 

duck  318 ;  turtle  229 
Jugulares  132 

Kangaroo  43 ;  dental  formula  423  ; 

lumbar  vertebrae  447 ;  pectineal 

process  513;  pes  522;  tail  453; 

teeth  345 
Kestrel,  claws  330 
Killer  45 ;  see  Orca 
Kiwi  40;  see  Apteryx 
Knee-cap,  see  patella 
Koala  43 ;   lumbar  vertebrae  447 ; 

pes  522;  tail  453 
Kiikentbal,  W.,  on  teeth  of  Cetacea 

426  ;  on  teeth  of  Marsupials  422 

Labial  cartilage,  dogfish  77;  Squa- 
tina  119 

Labridae  33 

Labrus  33 ;  see  Wrasse 

Labyrinthodontia  35  ;  buckler  168  ; 
general  characters  135 ;  inter- 
parietal  foramen  173  ;  pelvis  187; 
ribs  182  ;  skull  176  ;  teeth  169 

Lacertilia  37 ;  general  characters 
199 ;  pectoral  girdle  288  ;  skull 
277 ;  vertebrae  275 

Lachrymal  20;  cod  97;  crocodile 
251 ;  dog  394  ;  duck  317  ;  salmon 
93 

Lacunae  10 

Lagenorhynchus  45  ;  skull  462 

Lagostomus  47  ;  maxilla  477 

Lambdoidal  crest,  duck  315 

Lamella  of  malleus,  dog  393 

Lamuidae  32 

Lamprey  31,  55  f. 

Lancelot  30  ;  see  Amphioxus 

Laridae  42  ;  see  Gulls 

Larks  42 

Larvacea  30  ;  notochord  51 

Latax  48  ;  pes  526 

Lateral  ethmoid  21 ;  cod97;  salmon 
89  f. 

Leathery  turtle  37 ;  see  Derrno- 
chelys 

Lemuroidea  49;  caudal  vertebrae 
454  general  characters  372 ; 
nails  418  ;  ribs  493  ;  sacrum  452  ; 
skull  482  ;  thoraco-lumbar  verte- 
brae 450 ;  see  Lemurs 

E. 


Lemurs,  carpus  512 ;  pes  527 ; 
teeth  441  ;  see  Lemuroidea 

Lenticular  485  ;  dog  393 

Lepidosiren  34,  70;  branchial 
arches  125  ;  fins  130 

Lepidosteidae  33 

Lepidosteus  33;  attachment  of 
teeth  108 ;  distribution  66 ;  pec- 
toral fins  131 ;  scales  67,  104 ; 
skull  123  ;  tail  117  ;  vertebrae  68 

Lepidotus  33 ;  teeth  110 

Leporidae  48 

Lepospondyli  35 

Lepus  48  ;  see  Hare 

Leptoptilus  41  ;  see  Adjutant 

Lialis  37 ;  289 

Limbs,  general  account  26  ;  modifi- 
cations in  position  of  28  ;  rep- 
tiles 289 

Llama  45,  359  ;  cervical  vertebrae 
445  ;  skeleton  496  ;  teeth  428 

Limicolae  42 

Lingual  apparatus,  lampreys  58  ; 
myxinoids  57 

Lion  48 

Loemanctus  longipes,  shoulder  girdle 
and  sternum  287 

Loggerhead  turtle,  carapace  216 

Lophiodon  46  ;  teeth  345,  429 

Lophiodontidae  46 

Lophiomyidae  47 

Lophiomys  47  ;  pes  526  ;  skull  476 

Lophius,  attachment  of  teeth  107 

Lower  jaw  ;  see  Mandible 

Lumbar  vertebrae  16 ;  crocodile 
242  ;  dog  378  f.  ;  duck  311 

Lunar  27  ;  dog  408 

Macacus  49 ;  cervical  vertebrae  446 
Machaerodus  48;  upper  canines  437 
Macrauchenia  46,  358  ;  calcaneum 

360 ;     cervical    vertebrae     445  ; 

fibula  519;  tarsus  523  ;  ulna  501 
Macraucheniidae  46,  509 
Macropodidae     43,     350;     dental 

formula  423 ;  pes  522 
Macropus  43  ;  see  Kangaroo 
Macroscelidae  49 
Macroscelides  49  ;  skull  480 
Magnum  27  ;  see  Carpus 
Malar  22  ;  see  jugal 
Malleus,  dog  393 ;  man,  dog  and 

rabbit  485 

35 


546 


INDEX. 


Mammalia  42;  auditory  ossicles 
485  ;  cervical  vertebrae  442 ;  exo- 
skeleton  416  ;  general  characters 
343;  manus  503;  Mesozoic  — 348 ; 
pectoral  girdle  493  ;  pelvic  girdle 
512  ;  pes  521 ;  ribs  490  ;  sacral 
and  caudal  vertebrae  451 ;  skull 
455  ;  sternum  489  ;  thigh  and 
shin  517  ;  thoraco -lumbar  verte- 
brae 447 

Man  49  ;  arm  bones  503  ;  auditory 
ossicles  488  ;  caudal  vertebrae 
454  ;  cervical  vertebrae  446  ;  pel- 
vis 515  ;  pes  527  ;  ribs  493  ; 
scapula  499  ;  skull  483  ;  sternum 
490  ;  teeth  441 

Manatee  44  ;  see  Manatus 

Manatidae  44 

Manatus  44 ;  cervical  vertebrae  444 ; 
dental  formula  425 ;  humerus 
501  ;  manus  505  ;  pelvis  514 ; 
skull  460 ;  sternum  489  ;  teeth 
345 ;  thoraco-lumbar  vertebrae 
448 

Mandible,  birds  335  ;  cod  100  ; 
crocodile  258 ;  dog  398 ;  duck 
319  ;  frog  160 ;  Hippopotamus 
467  ;  Isabelline  bear  438  ;  newt 
144  ;  salmon  94  ;  turtle  230 

Manidae  44  ;  see  Manis 

Manis  44 ;  auditory  ossicles  487  ; 
manus  504  ;  scales  3,  417  ;  skull 
459  ;  M.  macrura  xiphisternum 
489  ;  see  Pangolin 

Manubrium  of  malleus  486  ;  dog 
393  ;  —  sterni,  dog  404 

Manus  26;  crocodile  265  ;  dog  408, 
413;  duck  323  ;  frog  164 ;  mam- 
malia 503  ;  newt  147  ;  Perisso- 
dactyles  5O8  ;  turtle  233 

Marginal  plate,  turtle  21 6  ;  —  ray 
131 ;  —  shield,  turtle  214 

Marmoset  49,  372  f. 

Marmot,  frontals  476 

Marsipobranchii  31,  53;  spinal 
column  56 

Marsupial  bones  513 

Marsupial  mole  43  ;  see  Notoryctes 

Marsupialia  43 ;  arm  bones  499 ; 
auditory  ossicles  486;  cervical 
vertebrae  443  ;  caudal  vertebrae 
453 ;  general  characters  349 ; 
manus  504  ;  pectoral  girdle  494  ; 


pelvis  513  ;  pes  521 ;  ribs  491  ; 
sacral  vertebrae  451  ;  skull  456  ; 
teeth  422  ;  thigh  and  shin  517  ; 
thoraco-lumbar  vertebrae  447 

Mastodon  47,  365  ;  teeth  434 

Mastodonsaurus  35, 136  ;  pelvis  187 

Mastoid  portion  of  periotic,  dog 
391 

Maxilla  22  ;  cod  98  ;  crocodile  254; 
dog  397  ;  duck  318  ;  frog  159  ; 
newt  144  ;  turtle  229 

Maxillo-mandibular  arch  21 

Maxillo-palatine,  duck  318 

Maxillo-turbinal,  dog  395 

Meatus,  external  auditory  — ,  cro- 
codile 250  ;  dog  393  ;  turtle  228 ; 
internal  auditory  — ,  crocodile 
251 ;  dog  392,  400  ;  turtle  228 

Meckel's  cartilage  22  ;  cod  100  ; 
dogfish  77  ;  salmon  94 

Median  ethmoid  21 ;  cod  98  ;  Gym- 
nophiona  179  ;   salmon   91 ;   - 
fin,  Amphibia  52  ;  cod  86  ;  dog- 
fish 79 

Megachiroptera  49 ;  general  charac- 
ters 371 

Megalobatrachus  35,  135 ;  carpus 
186 ;  skull  175 

Megalosauridae  38 

Megalosaurus  38,  208 

Megapodius,  spur  330 

Megaptera  44,  357 

Megatheriidae  44,  352 ;  humerus 
501 ;  leg  bones  517  ;  pelvis  513  ; 
sacrum  452  ;  teeth  424 ;  thoraco- 
lumbar  vertebrae  447 

Megatherium  44 ;  femur  517  ;  ma- 
nus 505  ;  pectoral  girdle  495  ; 
pes  522  ;  skull  458 

Megistanes  40,  299 

Membranous  cranium  17 

Menobranchidae  35 

Menobranchus  35, 135 ;  carpus  185 ; 
pes  188  ;  skull  174  ;  teeth  169 

Menopoma  35  ;  see  Cryptobranchu* 

Mento-meckelian  22  ;  frog  161  ; 
reptiles  284 

Merganser  41  ;  beak  329 

Mergus  41 

Merrythought,  duck  322 

Mesethmoid  20;  dog  390;  duck 
317 

Mesoplodon  44  ;  teeth  427 


INDEX. 


547 


Meso-pterygium  79 

Mesosauridae  37 

Mesosaurus  37 

Mesosternum,  dog  404 

Metacarpal  quill,  duck  303 

Metacarpo-digital,  duck  303 

Metacarpus  20  ;  see  Manus 

Metacromion,  hares  and  rabbits 
497 

Meta-pterygium  79 

Metatarsus  26  ;  see  Pes 

Metatheria  43  ;  general  characters 
349 

Metriorhynchus  39,  278 

Microchiroptera  49  ;  general  cha- 
racters 371 

Microgale  49  ;  caudal  vertebrae  454 

Mid-digital  quill,  duck  303 

Milk-teeth  344 ;  dog  377  ;  horse 
430 

Moa  40,  299 ;  aftershaft  328  ;  pec- 
toral girdle  336  ;  wing  338 

Molar  teeth  344  ;  dog  376  f. 

Mole  49,  370 ;  auditory  ossicles 
488  ;  cervical  vertebrae  446 ; 
humerus  503  ;  manus  512  ;  pre- 
sternum  490 ;  shoulder  girdle 
499 ;  skull  481 ;  teeth  440;  Golden 
—  49  ;  see  Chrysochloris ;  Mar- 
supial —  43 ;  see  Notoryctes 

Molge  35,  135  ;  see  Newt 

Monitor  38  ;  see  Varanus 

Monkey  49,  373;  see  under  Pri- 
mates 

Monodelphia  43  ;  characters  of  351 

Monodon  45,  357  ;  see  Narwhal 

Monophyodont,  defined  7  ;  344 

Monopneumona  34 

Monotremata  42  ;  arm  bones  499  ; 
auditory  ossicles  486 ;  caudal 
vertebrae  453  ;  cervical  vertebrae 
443 ;  general  characters  346 ; 
manus  504  ;  pectoral  girdle  493  ; 
pelvis  513  j  pes  521  ;  ribs  490  ; 
sacral  vertebrae  451  ;  skull  455  ; 
sternum  489  ;  teeth  422  ;  thigh 
and  shin  517 ;  thoraco-lumbar 
vertebrae  447 

Morosaurus  38,  207  ;  pes  294 

Mosasaurus  38,  204 

Moschus  46  ;  canines  429 

Mouse  47  ;  teeth  437  ;  see  lft/.s 

Mud-fish  34 


Multituberculata  43,  348 

Muntjac  46;  see  Gervulus 

Muraenidae  33 

Muridae  47 

Mus  47;  M.  musculus,  teeth  437  ;  M. 

sylvaticus,  sternum  and  shoulder 

girdle  498 

Musk  deer  46  ;  canines  429 
Mustelidae  48  ;  teeth  439 
Mycetes  49  ;  hyoid  485  ;  mandible 

484  ;  skull  482 
Myliobatidae  32  ;  teeth  109 
Myomorpha  47 
Mynnecobius,  teeth  423 
MyrmecopJiaga    44 ;    manus   505  ; 

pectoral  girdle  495  ;  skull  458 
Myrmecophagidae    44,     424 ;     see 

Anteaters 
Mystacoceti  44  ;  general  characters 

356 ;     hind    limb    518 ;    manus 

505  ;  pectoral  girdle  495  ;   skull 

461  ;  teeth  426 
Myxine   31,   55 ;    fins  115 ;    noto- 

chordal  sheath  9 
Myxinoidei  31,  55 

Nails  3  ;  Amphibia  168  ;  mammals 
417 

Nares:  anterior  — ,  crocodile  252, 
257;  dog  401 ;  duck  317;  newt  143; 
turtle  225,  229 ;  posterior  — ,  cro- 
codile 257  ;  dog  402  ;  duck  318  ; 
frog  158 ;  newt  143  ;  turtle  230 

Narial  cavity,  salmon  89 ;  —  pas- 
sage, crocodile  254  ;  dog  395; 
—  septum,  dog  401 

Narwhal  45,  357  ;  teeth  427 

Nasal  21 ;  crocodile  252  ;  dog  394  ; 
duck  317  ;  frog  158 ;  newt  143  ; 
turtle 228;  —capsule  20;  cod 97  ; 
crocodile  252 ;  dog  394  ;  dogfish 
74 ;  frog  158  ;  newt  143 ;  turtle 
228 ;  —  cavity,  dog  388 ;  —  fossae, 
salmon  89 ;  —  horns,  rhinoceros  3 

Navicular  27  ;  dog  414 

Neornithes  40  ;  general  characters 
298 

Nesodon  46,  361  ;  pes  525 ;  teeth 
432 

Nesodontidae  46 

Neural  arch  14 ;  —  plate,  turtle 
215  ;  —  spine  14 

Neuromere,  defined  112 

35—2 


548 


INDEX. 


Newt  35  ;  anterior  limb  147  ;  hyoid 
apparatus  or  visceral  arches  144, 
181  ;  pelvic  girdle  149  ;  ribs 
145  ;  shoulder  girdle  146  ;  skull 
140  ;  sternum  145  ;  vertebral 
column  138 

Notidanidae  31  ;  calcification  of 
vertebrae  114;  pectoral  fins  130; 
vertebral  column  113  ;  visceral 
arches  63,  119  f. 

Notochord,  Amphioxus  52  ;  Balano- 
glossusSO;  dogfish  72;  Tunicates 
51 

Nothosaurus  37,  193;  supratemporal 
fossae  283 

Nothosauridae  37 

Notoryctes  43  ;  arm  bones  500  ; 
caudal  vertebrae  453  ;  cervical 
vertebrae  443  ;  claws  418  ;  dental 
formula  423  ;  manus  504  ;  pelvis 
513  ;  pectoral  girdle  494  ;  pes 
521;  ribs  491;  sacrum  452; 
skull  457  ;  sternum  489  ;  thigh 
and  shin  517 

Notoryctidae  43,  350 

Nuchal  plate,  turtle  215  ;  —  shield, 
crocodile  238  ;  turtle  214 

Nyrania  35]  palatines  177 

Occipital  condyle,  crocodile  246  ; 
dog  386;  duck  315;  frog  154; 
turtle  224  ;  —  crest,  dog  386  ; 

—  segment,  crocodile  246;    dog 
384  ;  turtle  224 

Odontaspis  32  ;  succession  of  teeth 

1O7 

Odontoblast  7 
Odontoceti  44;  general  characters 

357  ;  manus  505  ;  pectoral  girdle 

495;   skull   462;    sternum   489; 

teeth  426 
Odontolcae  40  ;  general  characters 

299 

Odontopteryx  40;  jaws  334 
Ogmorhinus  48;  mandibular  ramus 

439 
Olecranon  process,  dog  406;  duck 

323  ;  frog  164 
Olfactory  capsule,  see  nasal  capsule  ; 

—  cavity,  dog  388  ;  —  chamber, 
dog  395  ;  —  fossa,  dog  390 


Omosaurus,  exoskeleton  272 


Omosternum,  frog  163 

Onychodactyliix  35 ;  nails  168 

Operculum,  cod  101 ;  salmon  95 

Ophidia  38 ;  general  characters  202 ; 
jaw  bones  280  ;  scales  270;  skull 
277  f. ;  vertebral  column  275 

Opliisaurus  38;  limbs  289;  pectoral 
girdle  289 

Opisthocoelous,  defined  14 

OpistJiocomus  41 ;  skull  334 

Opisthotic  20 ;  cod  96 ;  crocodile 
250  ;  salmon  89  f. ;  turtle  227 

Opossum  43;  caudal  vertebrae  453; 
teeth  423 

Optic  capsule  20 ;  crocodile  251 ; 
dog  394 ;  turtle  228 

Orang  49;  carpus  512;  ribs  493; 
thoraco-lumbar  vertebrae  450 

Orbit,  crocodile  257  ;  dogfish  74 ; 
duck  317 

Orbital  ring,  cod  97 ;  salmon  93 

Orbitosphenoid  19  ;  dog  388  ;  duck 
317 ;  newt  141 

Orca  45 ;  teeth  427 

Oreodon  45 ;  see  Cotylops 

Ornithodelphia  42 ;  general  charac- 
ters 346 

Ornithosauria  212 

Ornithorhynchidae  43 

Ornithorhynchus  43;  beak  3,  418; 
caudal  vertebrae  453 ;  manus 
504;  pelvis  513;  sacral  vertebrae 
451;  shoulder  girdle  347;  skull 
455 ;  spur  418  ;  tarsus  27  n. ;  teeth 
4,  346,  422  ;  thoraco-lumbar  ver- 
tebrae 447 

Ornithopoda  39 ;  general  characters 
209 

Orthopoda  39 ;  general  characters 
208 ;  pubes  292 

Orycteropodidae  44 ;  teeth  425 

Orycteropus  44 ;  hair  416 ;  manus 
505 ;  pectoral  girdle  495 ;  pelvis 
513;  skull  459  ;  see  Aard  Vark 

Osborn,  H.  F.,  on  Mesozoic  Mam- 
mals 348 

Os  entoglossum,  duck  320 

Osteoblast  11 

Osteoclast  11 

Osteodentine  108 

Osteostraci  31 ;  general  characters 
54 

Ostracion  33,  69  ;  plates  105 


INDEX. 


549 


Ostracionidae  33 

Ostracodermi  31 ;  general  charac- 
ters 54 

Ostrich  40,  299 ;  aftershaft  329; 
cervical  vertebrae  331;  claws 
330;  foot  342;  manus  338 ;  pelvic 
girdle  and  sacrum  34O ;  pubis 
341  ;  tibio-tarsus  341  ;  wing 
339 

Otaria  48;  dentition  439;  tym- 
panic bulla  480 

Otariidae  48,  369 ;  auditory  ossicles 
488  ;  scapula  498  ;  skull  480 

Owen's  apteryx,  pelvic  girdle  and 
sacrum  34 O 

Owen's  chameleon,  epidermal  horns 
271 

Owls  42,  335 ;  aftershaft  329 ;  foot 
342 

Owl-parrot  42  ;  see  Stringops 

Ox  46,  359;  atlas  and  axis  445; 
three  cervical  vertebrae  15 ;  fe- 
mur 518;  manus  507;  teeth 
345  ;  two  thoracic  vertebrae  449 

Paca  48 
Paired  fins  127 
Palaeoniscidae  32 
Palaeoniscus  32  ;  scales  67 
Palaeospondylidae  31 
Palaeospondylns  31,  58 
Palaeosyops  46 ;  teeth  432 
Palaeotheriidae  46 
Palaeotherium  46  ;  skull  471 ;  teeth 

430 

Palamedea  41 ;  spur  330,  338 
Palamedeae  41 
Palate,  reptiles  280  f. 
Palatine,   cod   98;   crocodile   254; 

dog   397;    duck   318;    frog  160; 

salmon  93  ;  turtle  230 
Palato  -  pterygo  -  quadrate    bar   22; 

dogfish  77;  fish  120  f.;   salmon 

93 

Palm  civet  48 
Pangolin  44 ;  pectoral  girdle  495 ; 

pelvis  513 ;  caudal  vertebrae  453 ; 

see  Mania 
Parachordals  17 
Paradoxurus  48;  tail  454 
Parasphenoid    21 ;    cod    97 ;    frog 

156 ;    newt    141 ;    reptiles   278  ; 

salmon  93 


Parasuchia  39 ;  general  characters 
211 

Parethmoid  21  n. 

Pariasauria  36 

Pariasaurus  36, 192;  pectoral  girdle 
289  ;  pelvis  292  ;  supratemporal 
fossa  283 ;  teeth  273 

Parietal    19 ;     cod    96 ;     crocodile 
247;  dog  386;  duck  314;  newt 
141 ;  salmon  91 ;  turtle  225  ;  - 
segment,  crocodile  247  ;  dog  386 ; 
turtle  225 

Paroccipital  process,  dog  386 

Parr  a  42  ;  spur  330 

Parrots  335;  aftershaft  328;  beak 
330;  epiphyses  of  centra  332; 
foot  342 ;  powder-down  feathers 
329 ;  skull  334 

Parrot  fish  33 ;  see  Scans 

Passeres,  aftershaft  328 

Passeriformes  42 

Patella,  dog  412  ;  duck  327 

Pavo  41 ;  P.  cristatus,  shoulder 
girdle  and  sternum  337 

Peacock  41 ;  see  Pavo 

Peccary,  pes  523 

Pecora  46,  359 ;  teeth  429 

Pectinated  incisors,  Galeopjthecus 
370,  440 ;  Procavia  362 

Pectineal  process,  duck  326 

Pectoral  fins,  cod  103  ;  dogfish  79  ; 
—  girdle  24;  Amphibia  184; 
birds  336;  cod  101;  crocodile 
262;  dog  404;  dogfish  79;  duck 
321;  fish  126;  frog  162;  mam- 
malia 493;  newt  145;  reptiles 
288  ;  turtle  231;  —  shield,  turtle 
215 

Pedetes  47;  manus  511;  tail  454 

Pelican  41,  335  ;  clavicles  338 

Pelicanus  41 ;  P.  conspicillatus 
shoulder  girdle  and  sternum 
337 

Pelobates  36;  vertebrae  172;  P. 
cultripes  teeth  169 

Pelobatidae  36 

Pelvic  tins,  cod  103;  dogfish  82; 
fish  131 ;  —  girdle  25 ;  Amphi- 
bia 187 ;  birds  339 ;  crocodile  266 ; 
dog  409;  dogfish  81;  duck  324; 
fish  127 ;  frog  165 ;  mammals 
512;  newt  149;  Eatitae  34O; 
Reptilia  291 ;  turtle  235 


550 


INDEX. 


Penguin  40 ;  distribution  of  feathers 
328 ;  fibula  341 ;  foot  342 ;  manus 
338;  metatarsus  342;  pneuma- 
ticity  of  skeleton  331;  skull  333; 
sternum  336 ;  thoracic  vertebrae 
332  ;  wing  329,  339 

Penna,  duck  303 

Pentedactylate,  denned  26 

Perameles  43;  atlas  443;  pectoral 
girdle  494 

Peramelidae  43,  350;  auditory  os- 
sicles 486;  pes  522 

Perca  34 

Perch  34  •  pelvic  fin  132 ;  urostyle 
117 

Percidae  34 

Perennibranchiata  35',  characters 
135 

Perichondrium  10 

Perichordal  sheath  16 

Periosteal  ossification  10 

Periosteum  10 

Periotic,  dog  390;  —  capsule,  see 
Auditory  capsule 

Perissodactyla  46;  cervical  verte- 
brae 445;  general  characters 
359 ;  manus  507 ;  pes  523  ;  ribs 
491;  scapula  496;  skull  470; 
teeth  429 ;  thoraco-lumbar  ver- 
tebrae 448 

Persistent  pulps  5 

Pes  26;  crocodile  268;  dog  413, 
414 ;  duck  327 ;  frog  166 ;  mam- 
mals 521;  reptiles  293;  turtle 
236  ;  of  Tapir,  Ehinoceros,  Hip- 
parion  and  Horse  524 

Petromyzon  31,  55  f. ;  notochordal 
sheath  9 

Petromyzontidae  31,  55 

Petrous  portion  of  periotic,  dog 
391 

Pezophaps  42;  see  Solitaire 

Phacochaerus  45 ;  teeth  428 

Phaethon  41 ;  metatarsals  342 

Phalacrocorax  41 

Phalangeridae  43,  350 

Phalanges  26 ;  see  Manus  and 
Pes 

Phaneroglossa  36 

Pharyngo-branchial,  cod  101 ;  dog- 
fish 78 ;  salmon  95 

Pharyngognathi  33 

PJiascolarctus  43 ;  see  Koala 


Phascolomyidae  43,  350 

Phascolomys  43,  349 ;  see  Wombat 

Phascolotherium  43,  348 

Phenacodontidae  47 

Phenacodus  47,  362 ;  caudal  ver- 
tebrae 454;  manus  51O;  pes 
525  ;  scapula  497 ;  skull  472 ; 
thoraco-lumbar  vertebrae  449 

Phocaena  45,  357;  skull  462;  tho- 
raco-lumbar vertebrae  448 ;  P. 
phocaenoides,  ossicles  420 

Phocidae  48,  369;  scapula  497; 
tympanic  bulla  480 

Phoronis  30,  50  f . 

Phororhacos  41 ;  anterior  nares 
333;  ischia  341 

Physeter  44 ;  cervical  vertebrae 
444;  manus  505;  skull  464;  teeth 
426 

Physeteridae  44;  ribs  491;  thoraco- 
lumbar  vertebrae  448 

Physodon  44  ;  teeth  426 

Physodontidae  44 

Physostomi  33 

Phytosauridae  39 

Phytosaurus  39;  see  Belodon 

Pici  42 

Picus  42;  see  Woodpecker 

Pig  45,  359;  skull  465  f.,  466; 
teeth  345,  427 

Pigeons  42,  334  f. ;  aftershaft  329 ; 
pneumaticity  of  skeleton  331 

Pike  33;  pelvic  fin  132;  teeth  107, 
110 

Pinnipedia  48;  arm  bones  502; 
auditory  ossicles  488 ;  general 
characters  369 ;  manus  511 ; 
pelvis  515;  pes  526;  skull  480; 
teeth  439 ;  thigh  and  shin  520 ; 
thoraco-lumbar  vertebrae  450 

Pipa  36 ;  hyoid  apparatus  182 ; 
jaws  169;  skull  180;  sternum 
184 ;  vertebrae  172 

Pipidae  36 

Pisces  31 ;  general  characters  60 

Piscivorous  dentition  426,  440 

Pisiform  345,  504;  crocodile  265; 
dog  408  ;  turtle  233 

Pituitary  fossa,  crocodile  247 ;  — 
space  17 

Placodontia  36 

Placodus  36,  192;  teeth  273 

Placoid  scale  4,  60,  104 


INDEX. 


551 


Plantigrade,  defined  358  n. 

Plastron,  Dermochelys  272;  Che- 
lone  midas  217,  218,  271 

Platanistidae  45 

Platanista  45,  cervical  vertebrae 
444 ;  skull  464 

Plectognathi  33 ;  vertebrae  115 

Plectroptertis  41 ;  P.  gambensis, 
spur  330 

Plesiosauridae  37;  limbs  193  ;  para- 
sphenoid  192 ;  skull  278 

Plesiosaurus  37,  193 ;  position  of 
limbs  28 

Pleuracanthidae  63 ;  fins  115 

Pleurodira  37-,  general  characters 
195 

Pleurodont,  159,  199,  273 

Pleuronectidae  33 

Pleuropterygii  31,  63 

Pliosaurus  37,  193 

Plovers,  42,  334 ;  thoracic  verte- 
brae 332 

Pneumaticity  of  bird's  skeleton  331 

Polacanthus  39',  exoskeleton  272 

Pollex  26 ;  see  Manus 

Polyodoji  32,  104 ;  distribution  66 ; 
pectoral  fins  131;  skull  122; 
spinal  column  112  ;  teeth  110 

Polyodontidae  32 

Polyonax  39,  209;  beak  271; 
frontals  277;  jaw  274 ;  predentary 
284 

Polyprotodont  423 

Polyprotodontia  43',  general  cha- 
racters 350 

Polypteridae  33 

Polypterus  33,  68 ;  distribution  66 ; 
exoskeleton  67;  pectoral  fins 
131 ;  pelvic  fins  132 ;  pelvis 
127 ;  scales  104 ;  skull  122  ;  tail 
116 

Pontoporia  45;  cervical  vertebrae 
444;  teeth  426 

Porcupine  47;  pes  526;  skull  476, 
477  ;  spines  417 

Porpoise  45,  357;  thoraco-lumbar 
vertebrae  448 

Postaxial  28 

Posterior  cornu,  duck  320;  turtle 
231;  —limb  26;  Amphibia  188; 
birds  341 ;  dog  412 ;  duck  326 ; 
frog  166;  newt  149,  148 ;  reptiles 
293;  turtle  235,  234 


Postfrontal  21 ;  crocodile  250  ; 
turtle  225 

Postorbital  bar,  crocodile  250, 
255  f.;  Hatteria  283;  —  groove, 
dogfish  76 

Post-temporal,  cod  102 ;  reptiles 
283 ;  —  bar,  crocodile  256  ;  Hat- 
teria 283 

Potamogale  49,  367,  370;  shoulder 
girdle  499;  teeth  440 

Potamogalidae  49 

Powder-down  feathers  329 

Pre-axial  28 

Precoracoid  25 ;  frog  163 ;  newt  147 ; 
reptiles  288 ;  turtle  232 

Predentary,  reptiles  284 

Predigital  quill,  duck  303 

Prefrontal  21 ;  crocodile  249 ;  rep- 
tiles 278 ;  turtle  225 

Prefronto-lachrymal,  newt  141 

Prehallux,  frog  167  f. 

Premaxilla  22;  cod  98;  crocodile 
252;  dog  398;  duck  314,  318; 
frog  158;  newt  143;  salmon  94; 
turtle  230 

Premolar,  dog  370,  377;  mammals 
344 

Prenasal  process,  frog  158 

Pre-orbital  vacuity,  reptiles  283 

Presphenoid  19  ;  dog  388 

Prespiracular  ligament,  dogfish  77 

Presternum,  dog  404 

Primaries,  duck  303 

Primates  49;  arm  bones  503;  au- 
ditory ossicles  488 ;  cervical  ver- 
tebrae 446;  general  characters 
372;  manus  512;  pelvis  515; 
pes  527;  ribs  493;  sacrum  452; 
shoulder  girdle  499 ;  skull  482  f . ; 
sternum  490 ;  tail  454 ;  teeth 
441 ;  thigh  and  shin  520  ;  thora- 
co-lumbar vertebrae  450 

Priodon  44 ;  caudal  vertebrae  453 ; 
manus  505 ;  stapes  487  ;  sternum 
489  ;  teeth  424 

Pristidae  32 

Pristis  32;  snout  or  rostrum  109, 
119 

Proboscidea  47;  arm  bones  502; 
cervical  vertebrae  445 ;  general 
characters  364 ;  femur  519 ;  ma- 
nus 511;  pelvis  514;  pes  526; 
scapula  497;  skull  473;  teeth 


552 


INDEX. 


433; 
449 


thoraco-lumbar    vertebrae 


Procavia  47,  363;  auditory  ossicles 
487;  caudal  vertebrae  453;  dental 
formula  432  ;  humerus  502;  ma- 
nus  51O;  pelvis  514;  pes  525; 
ribs  491 ;  scapula  497 ;  skull 
433,  472;  tarsus  27;  thoraco- 
lumbar  vertebrae  449 

Process,  alinasal  — ,  firog  158 ; 
basi-pterygoid  — ,  birds  334 ; 
coracoid  — ,  dog  405;  coronoid 

—  (of  mandible),  dog  398;  duck 
319;   coronoid  —  (of  ulna),  dog 
408 ;  pectineal  — ,  duck  326 ;  post- 
frontal  — ,  duck  316;    postgle- 
noid  — ,  dog  394 ;  postorbital  — 
(of  frontal),  dog  388;  postorbital 

—  (of  jugal),  dog  398;  posterior 
articular    — ,    duck    319;    zygo- 
matic  — ,  dog  394 

Processus  brevis,  486;  —  gracilis 

486;  —  longus,  486;  dog  393 
Procoelous,  defined  14 
Prodelphinus  45;  skull  462 
Proganosauria  37 
Prone  position  29 
Prongbuck  46  ;  horns  417 
Pro-otic  20;  frog  157;  turtle  227 
Pro-pterygium,  dogfish  79 
Proteidae  35 
Proteles  48;  teeth  437 
Protelidae  48 
Proterosauridae  37 
Proterosaurus  37;  teeth  198,  274; 

vertebrae  197 
Proteus    35,    135,    182;    branchial 

arches  180 ;  digits  187 ;  pes  188 ; 

skull  174 
Protoptervs  34,  70.  117;  branchial 

arches  121,  124;  fins  130;  skull 

124;    vestigial   gill  on   pectoral 

girdle  129 
Prototheria  42;  general  characters 

346 

Proximal,  defined  23  n. 
Psephurus,  distribution  66 
Pseudopus  38 ;  limbs  289 
Psittaci  42;  see  Parrots 
Pteranodon  39,  274 ;  pectoral  girdle 

289 

Pteranodontidae  39 
Pteraspis  31,  54 


Pterichthys  31,  55 

Pterocles  42  ;  see  Sandgrouse 

Pteroclidae  42 

Pterodactylidae  39 

Pterodactylus  39,  213 

Pteropidae  49;  skull  481 

Pteropus  49;  dental  formula  441; 

tail  454    ' 
Pterosauria  39;  general  characters 

212;  ischia  292;  limbs  291;  pre- 

orbital   vacuity   284;    ribs   285; 

sternum  287  ;  vertebrae  275  f. 
Pterotic  20;  cod  96;  salmon  90  f. 
Pterygoid,  cod  98;    crocodile  255; 

dog   397;   duck   318;   frog  160; 

newt  144 ;  salmon  93  ;  turtle  230 ; 

—  fossa,  crocodile  255  ;  —  plate, 

dog  388 
Pterylae  328 
Pubis   25;    crocodile   266 f.;    duck 

325;    dog  411;    frog  165;    newt 

149;  reptiles  292  ;  turtle  235 
Pygal  plate,  turtle  217 ;  —  shield, 

turtle  214 
Pygopodidae  37 
Pygostyle,  duck  307,  312 
Python  38;  ischio-pubis  292;  jaws 

280 ;  vestiges  of  limbs  289,  293 
Pythonomorpha   38;  general   cha- 
racters  204;    limbs   290;    teeth 

273 

Quadrate  22;  cod  98;  crocodile 
255;  duck  319;  frog  160;  newt 
144 ;  salmon  93 ;  turtle  229 

Quadratojugal  22  ;  crocodile  255 ; 
duck  318;  frog  160;  turtle  229 

Quill,  duck  302 

Babbit  48,  366;  pollex  511 
Kaccoon  369 
Eachis,  duck  302 
Kachitomous,  defined  171 
Eadiale  27 ;  see  Carpus 
Eadialia  115;  dogfish  79  f. 
Eadio-ulna,  frog  164 
Eadius  26;  crocodile  265;  dog  406; 

duck  323 ;  newt  147 ;  turtle  233 
Raia  32 ;  calcification  of  vertebrae 

114 

Eaiidae  32 
Eana  36  ;  see  Frog 
Eanidae  36;  shoulder  girdle  185 


INDEX. 


553 


Eat,  pes  526 

Eatitae  40;  caudal  vertebrae  333; 
clavicles  338;  foot  342;  general 
characters  298;  skull  333;  ster- 
num 336 ;  vomers  334 ;  wing  338 

Eattlesnake  38;  rattle  3,  270 

Eay,  pectoral  fin  130;  Eagle  — , 
Electric  —  and  Sting  — ,  32 

Eectrices,  303,  329 

Eeed-fish  33 

Eeindeer,  antlers  469 

Eemicle,  duck  304 

Eemiges,  303,  329 

Eeptiles,  anterior  limb  290;  exo- 
skeleton  270;  fossae  in  skull  281 ; 
pectoral  girdle  288 ;  pelvic  girdle 
291;  posterior  limb  293;  ribs 
285;  skull  276;  sternum  287; 
teeth  272 ;  vertebral  column  275 

Eeptilia  36 ;  general  characters  190  ; 
see  Eeptiles 

Rhabdopleura  30,  50 

Rhamphastos  42;  see  Toucan 

Ehamphorhynchidae  39 

Rhamphorhynchus  39,  213,  274 

Rhea  40]  aftershaft  329;  claws 
330;  ischia341;  manus  338;  R. 
macrorhyncha,  pelvic  girdle  and 
sacrum  34  O 

Eheornithes  40 

Rhina  32 ;  see  Squatina 

Ehinal  process,  frog  158 

Rhinoceros  46,  360,  419;  femur 
518;  fibula  519;  malleus  487; 
manus  508;  nasal  horns  3,  417; 
pes  525;  skull  421,  470;  teeth 
430;  ulna  501;  R.  antiquitatis 
470 

Ehinocerotidae  46 

Ehinolophidae  49 

Ehiptoglossa  38 

Ehizodontidae  33 

Rhizodus  33;  teeth  110 

Ehynchocephalia  37;  general  cha- 
racters 197 ;  humerus  290 ;  teeth 
273  f. ;  vertebrae  275 

Ehynchosauridae  37 ;  maxillae  198 

Rhytina  44,  352,  425;  humerus 
501 ;  skull  460 

Ehytinidae  44 

Eibs  23;  Amphibia  182;  birds  336; 
cod  86  ;  crocodile  259  ;  dog  402  ; 
dogfish  73 ;  duck  320 ;  fish  125 ; 


frog  153;  mammalia  490;  newt 
145 ;  reptiles  285 

Eidge,  supra-orbital  andsuborbital, 
dogfish  74 

Eodentia  47 ;  auditory  ossicles  488 ; 
cervical  vertebrae  446 ;  dental 
formula  435  ;  general  characters 
365  ;  pelvis  515  ;  pes  526  ;  hume- 
rus 502;  manus  511;  ribs  493; 
sacrum  452;  shoulder  girdle  497 ; 
skull  476;  sternum  489;  tail 
454;  teeth  421;  thigh  and  shin 
520 ;  thoraco-lumbar  vertebrae 
449 

Eoller  42,  335 

Eooted  teeth,  defined  5 

Eorqual  44,  357 ;  cervical  vertebrae 
444 

Eostrum,  crocodile  247;  dogfish 
74;  duck  316;  Pra«i«119;  —of 
sternum,  duck  321 

Eose,  C.,  on  teeth  of  Marsupials 
422 

Euminantia  46,  359;  auditory  os- 
sicles 487;  fibula  519;  horny 
plates  on  palate  418;  hyoid  470; 
manus  507 ;  odontoid  process 
445  ;  pes  523 ;  scapula  495 ;  teeth 
420,  429 

Sabre-toothed  lion  48,  see  Machac- 
rodus 

Sacral  ribs,  crocodile  243 ;  —  sur- 
face of  ilium,  dog  409 ;  —  verte- 
brae 16;  crocodile  243;  dog  383; 
duck  312;  frog  153;  newt  140; 
turtle  222 

Sacrum,  duck  310 ;  see  Sacral  ver- 
tebrae 

Sagittal  crest,  dog  386 

Saiga,  skull  468 

Salamander  35 

Salamandra  35,  135;  antibrachium 
and  manus  of  larva  186  ;  manus 
of  larva  185  ;  tarsus  27 

Salamandrina  35,  135 ;  skull  175 ; 
sternum  182 

Salmo  33 

Salmon  33 ;  branchial  arches  95 ; 
chondrocranium  87 ;  opercular 
bones  95;  pectoral  fins  131 ;  skull 
87 

Salmonidae  33 


554 


INDEX. 


Sandgrouse  42,  335 
Sarcophilus  43 ;  teeth  423 
Sauropoda  38;  general  characters 

205  ;  teeth  273  ;  vertebrae  276 
Sauropsida  36 ;  general  characters 

189 

Sauropterygia  37-,  general  charac- 
ters 192;  limbs  290;  palate  281; 

pectoral    girdle    288;    vertebrae 

276 

Saw-fish  32 ;  see  Pristis 
Scales,    cod    83;     crocodile    237; 

ctenoid  8 ;  cycloid  8  ;  duck  302  ; 

ganoid   8  ;    Gymnophiona   168  ; 

mammals  417 
Scale-foot  37 
Scalpriform  366 

Scaphirhynchus  32,  104 ;  distribu- 
tion 66;  exoskeleton  67;   spinal 

column  112 

Scaphoid  27  ;  mammals  504  f. 
Scapho-lunar,  dog  408 
Scapula  25 ;  cod  103;  crocodile  263 ; 

dog   404;   duck   322;   frog  162; 

newt  146  ;  turtle  232 
Scapular  shield,  armadillo  419 
Scapus,  duck  302 
Scarus  33;  beaks  111 
Scelidosauridae  39 
Schizognathous,  defined  335 
Scincidae  38 
Scincus  38 ;  scutes  271 
Sciuromorpha  47 
Sclerotic,  turtle  228 
Screamer  41 ;  spurs  330 
Scutes,  armadillos   419 ;   crocodile 

237 ;  reptiles  271 
Scylliidae  32 

Scyllium  32;   calcification  of  ver- 
tebrae  114  ;    pectoral  fins   130  ; 

suspensorium  119 ;  see  Dogfish 
Scymnus  32,  118;   calcification  of 

vertebrae  114 ;  mandibular  arch 

120 ;  pectoral  fins  130 
Scythrops  42 ;  interorbital  septum 

333 
Sea  leopard  48 ;   see  Ogmorhinus ; 

—  lion  48;  manus  511 ;  pes  526 ; 

position  of  limbs  29 ;    —  otter 

48;  pes  526 
Seal   369;    manus   511;    pes   526; 

sacral    vertebrae    452 ;     scapula 

497 


Secondaries,  duck  303  f. 
Secretary-bird  41 ;  claws  330 
Selachii  31 ;  general  characters  63 ; 

teeth  108 

Selenodont,  defined  345,  428 
Sella   turcica,   crocodile  247 ;   dog 

386 

Semionotidae  33 
Semiplumae  328 
Sense  capsules,  see  Auditory,  Nasal 

and  Optic  capsule 
Seps  38  ;  limbs  289 
Shagreen  61 
Shaft  of  feather  302 
Shark  64;  Frill-gilled  —  31\   see 

Chlamydoselache ;    Port  Jackson 

—  32 ;  see  Cestracion 
Sheep  359 ;  manus  507  ;  teeth  345 
Shields  of  turtle  214 
Shin  26 ;  see  Crus 
Shoulder  girdle,  see  Pectoral  girdle 
Shrew  49,   370;    auditory  ossicles 

488  ;  cervical  vertebrae  446  ;  pre- 

sternum  490;    skull  481;   teeth 

440 

Sigmoid  notch,  dog  406 
Siluridae  33 ;  plates  105 
Simla  49 ;  ribs  493 ;  skull  484 

thoraco-lumbar  vertebrae  450 
Simiidae  49,  373 
Simplicidentata  47,  366 
Siphonops  35;  S.  annulatus,  skull 

178 
Siredon  35  ;  skull  175  ;  teeth  169  ; 

visceral  arches  181 
Siren  35,   135,   188;    beaks   168; 

branchial  arches  180 ;  digits  187 

skull  174 ;  teeth  169 
Sirenia  44,  522 ;   arm  bones  501 ; 

caudal  vertebrae    453 ;    cervical 

vertebrae  443 ;  general  characters 

352 ;  hair  416 ;  horny  plates  418 ; 

manus  505  ;  pectoral  girdle  495  ; 

pelvis  514 ;  ribs  491 ;  skull  459 ; 

sternum  489 ;  teeth  425 ;  thoraco- 
lumbar  vertebrae  448 
Sirenidae  35 
Sirenoidei  34;   general   characters 

70 

Sivatherium  46 ;  skull  469 
Skate  32 
Skeletogenous  layer  14,  16;  Amphi- 

oxus  52,  112 


INDEX. 


555 


Skeleton,  defined  1 ;  Cape  Buffalo 
492 ;  Ceratodu*  128  ;  cod  83  f. ; 
crocodile  237  f . ;  dog  374  f . ;  duck 
302  f. ;  frog  151  f. ;  llama  496  ; 
newt  138  f. ;  turtle  214  f. 

Skink  38 ;  see  Tiliqua 

Skull  16  f. ;  Amphibia  173  f . ;  Anura 
179  f.;  birds  333  f.;  cod  96  f.; 
crocodile  243  f.  ;  diagram  of 
Mammalian  385  ;  Dipnoi  124 ; 
dog  383  f. ;  dogfish  73  f. ;  donkey 
431 ;  duck  312  f. ;  fish  117;  frog 
154  f.,  159  ;  Globicephalus  463  ; 
Gymnophiona  177;  Indian  ele- 
phant 474 ;  Mammalia  455 ; 
Marsipobranchii  57;  pig  466; 
Procavia  433  ;  reptiles  276  f. ; 
Ehinoceros  421 ;  Rhytina  46O ; 
sloth  458  ;  Tasmanian  wolf 
456 ;  Teleostei  124;  turtle  222  f.; 
wombat  456 

Sloth  43,  352 ;  auditory  ossicles 
487  ;  arm  bones  500  ;  claws  418 ; 
leg  bones  517;  manus  505;  pec- 
toral girdle  495  ;  pelvis  513 ;  pes 
522;  ribs  491;  sacrum  452;  skull 
457;  sternum  489;  teeth  424; 
thoraco-lumbar  vertebrae  447 

Snake  38 ;  see  Ophidia 

Sole  33 

Solea  33 

Solenodon  49 ;  teeth  440 

Solenodontidae  49 

Solitaire  42,  330 ;  wing  338 ;  wrist 
330 

Sorex  49;  pelvis  515;  see  Shrew 

Soricidae  49 ;  skull  481 

Spalacidae  47 

Spatularia  32 ;  distribution  66 

Spelerpes  35 ;  branchial  arches  180 ; 
ribs  182 ;  S.  belli  teeth  169 

Sperm  whale  44,  357 ;  see  Physeter 

Sphargis  37;  see  Dermochelys 

Sphenethmoid,  frog  156 

Sphenisci  40 ;  see  Penguins 

Sphenisciformes  40 

Sphenodon  37,  197  f. ;  carpus  291 ; 
cervical  vertebrae  275 ;  fossae  in 
skull  281;  humerus  290;  inter- 
parietal  foramen  277;  ribs  286; 
skull  282;  tarsus  293;  teeth 
274 

Sphenodontidae  37 


Sphenoidal  fissure,  dog  388 

Sphenotic  20 ;  cod  97 ;  salmon 
89 

Spider  monkey  49;  see  Ateles 

Spinacidae  32 

Spinal  column  13 ;  Dipnoi  113 ; 
fish  112  ;  Holocephali  113 ;  Mar- 
sipobranchii 56 

Spines,  Elasmobranchs  61 ;  mam- 
mals 417 

Spiny  anteater  43 ;  see  Echidna ; 
—  mouse  47 ;  see  Acanthomys 

Splenial  22;  crocodile  258;  duck 
320 ;  turtle  231 

Spurs,  birds  330;  Monotremata 
418 

Spur- winged  goose  330 ;  —  plover 
330 

Squalidae  31,  64 

Squalodon  45,  357  \  dental  formula 
427 

Squalodontidae  45 

Squamata  37;  general  characters 
198 ;  position  of  teeth  272 ;  skull 
278 

Squamosal  21 ;  crocodile  256 ;  dog 
394;  duck  316;  frog  160;  newt 
144 ;  turtle  229 

Squatina  32 ;  calcification  of  ver- 
tebrae 114;  labial  cartilages  119; 
tail  63 ;  vertebral  column  114 

Squatinidae  32 

Squirrels,  frontals  476 ;  pes  526 

Stapes,  dog  393;  frog  157;  man, 
dog,  rabbit  485 ;  newt  141 

Steganopodes  41 

Stegosauria  39 ;  general  characters 
209 

Stegosauridae  39 

Stegosaurus  39,  208  f. ;  exoskeleton 
272 

Steller's  sea-cow  44 ;  see  Rhytina 

Stereornithes  41 

Stereospondyli  35 

Sternal  ribs,  crocodile  259 ;  dog 
402  ;  duck  320  ;  mammals  490  f. 

Sternebra,  dog  404 

Sternum  24  ;  Amphibia  182  ;  birds 
336;  crocodile  260,  261;  dog 
403 ;  duck  321  ;  frog  163 ; 
Mammalia  489;  newt  145;  rep- 
tiles 287 

Stork  335 ;  White  —  41 


556 


INDEX. 


Striges  42 ;  see  Owls 

Stringops  42 ;  sternum  336 

Struthio  40,  299 ;  see  Ostrich 

Struthiornithes  40,  299 

Sturgeon  32 ;  see  Acipenser 

Stylo-hyal,  dog  399 

Suborbital  bar,  duck  318 ;  —  ridge, 

dogfish  76 

Subplantigrade,  defined  358  n. 
Subungulata  46;    arm  bones  502; 

general  characters  360 ;    manus 

509;  pelvis  514;  pes525;  shoulder 

girdle  497 ;  skull  471 ;  teeth  432 ; 

thigh  and  shin  519 
Suidae  45 
Suina  45,  358  f. ;  fibula  519 ;  manus 

507;  odontoid  process  445 ;  pelvis 

514;  pes  523;  ulna  501 
Sula  41 ;  see  Gannet 
Supinator  ridge,  dog  406 
Supine  position,  defined  29 
Supra-angular  22 ;    crocodile   258  ; 

duck  319 ;  turtle  230  f. 
Supracaudal  shield,  turtle  214 
Supraclavicle,  cod  102 
Supra- occipital  19;  crocodile  247; 

dog  386 ;  duck  315 ;  turtle  224 
Supra-orbital  20  ;  crocodile  251 
Suprapharyngeal  bone,  cod  101 
Suprascapula,  crocodile  263 ;  frog 

162 
Supratemporal    arcade,    crocodile 

256 ;  reptiles  281 
Surinam  toad  36 ;  see  Pipa 
Sus  45;   dental  formula  428;    see 

Pig 

Suspensorium,  Amphibia  173;  dog- 
fish 78 ;  duck  319 ;  frog  160  ;  newt 

144 ;  Pisces  61 
Sutures  12 
Swan    41;    cervical    and   thoracic 

vertebrae  332 
Swift  42,  335 ;  foot  342 
Symplectic,  cod  100 ;  salmon  94 

Tails,  fish  60 

Talpa  49;  pelvis  515;  see  Mole 

Talpidae  49 

Tapir  46,  360;    malleus   487;   pes 

524,  525 ;  teeth  345 ;  see  Tapirus 
Tapiridae  46 ;  dental  formula  429 
Tapirus    46 ;    fibula   519 ;    manus 

508 ;  skull  471 ;  see  Tapir 


Tarsier  49 

Tarsiidae  49 

Tarsipes  43,  349 ;  mandible  457 

Tarsius,  49,  372 ;  pes  527 

Tarso-metatarsus,  duck  327 

Tarsus  26  f. ;  crocodile  268 ;  dog 
414;  frog  166;  newt  150;  turtle 
236 

Tasmanian  devil,  43;  see  Sarco- 
pliilus;  — wolf  43;  see  Thylacinus 

Tatusia  44 ;  stapes  487  ;  teeth  424 

Tectospondyli  114 

Tectrices,  duck  306 

Teeth  6  ;  Amphibia  169  ;  birds  330; 
cod  83;  crocodile  238;  develop- 
ment 7  ;  dog  374  f. ;  fish  106 f. ; 
frog  158  f. ;  horses  5 ;  mammals 
344,  420  f. ;  pharyngeal  8 ;  rep- 
tiles 272  f . ;  structure  4 ;  succes- 
sion 7 

Teleosauridae  39 

Teleosaurus  39  ;  palate  281 ;  scutes- 
271 ;  vertebrae  275 

Teleostei  33 ;  general  characters 
69;  ribs  126;  skull  124;  tail 
117;  teeth  110;  vertebral  column 
115 

Temnospondyli  35 

Tenrec  49;  see  Centetex 

Tentorium,  dog  392 

Terrapin  37 

Testudo  37,  194 

Tetraceros  46 ;  horns  417 

Thalassochelys,  carapace  216 

Thecodont,  defined  273 

Theriodontia  36 

Theromorpha  36;  general  charac- 
ters 191;  humerus  290;  pectoral 
girdle  288;  ribs  285;  skull  278; 
teeth  273 ;  vertebral  column  275  f . 

Theropoda  38;  general  characters 
207 ;  teeth  273 

Thoracic  ribs,  crocodile  259;  see 
Bibs  ;  —  vertebrae  16 ;  crocodile 
241,  242;  dog  381,  382;  duck 
310;  turtle  221 

Thoraco- lumbar  vertebrae,  mam- 
mals 447  f. 

Thornback  skate  104 

Thylacinus  43;  atlas  443;  dental 
formula  423;  pelvis  513;  pes. 
521 ;  skull  456 

Thylacoleo  43;  skull  457 


INDEX. 


557 


Thyro-hyal,  dog  399 

Tibia  26;  crocodile  268;  dog  412; 

newt  149 ;  turtle  235 
Tibiale  27;  see  Tarsus 
Tibio-fibula,  frog  166 
Tibio-tarsus,  duck  326 
Tichorhine  Khinoceros  470 
Tiger  48 

Tiliqua  38;  scutes  200,  271 
Tillodontia    47,    365;    femur   520; 

manus  511 ;  teeth  435 
Tinamidae  300;   caudal   vertebrae 

333 ;  vomers  334 
Tinamiformes  41 
Tinamus  41 ;  ischia  341 
Titanotheriidae46;  skull  470;  teeth 

432 
Titanotherium  46;    humerus   501; 

manus  5O8  ;  pes  525 
Toad  36 ;  shoulder  girdle  185 
Tope  32 

Torpedinidae  32 
Torpedo  32,  104 

Tortoise  37;  position  of  limbs  28 
Tortrix,    ischio-pubis   292;    traces 

of  posterior  limb  203 
Toucan  42;  foot  342 
Toxodon  46,   361;  femur  519;  pes 

525  ;  teeth  432 
Toxodon tia  46;  general  characters 

361 ;  manus  509;  skull  472;  teeth 

432 

Toxodontidae  46 
Trabeculae  11;  —  cranii  17 
Tragulidae  45 
Tragulina    45,    359;     fibula    519; 

manus    507 ;    odontoid    process 

445;  pes  523;   skull  468;  teeth 

429;  ulna  501 

Transpalatine,  crocodile  255;  rep- 
tiles 278 

Trapezium  27 ;  dog  408 
Trapezoid  27 ;  dog  408 
Trichechidae,  48,  369 
Trichechus  48;  see  Walrus 
Triouychia  37 ;  general  characters 

194 

Trionychidae  37 
Triomjx    37,    193  f.  ;    exoskeleton 

214,  270;  skull  283;  vestiges  of 

teeth  274 

Trixaolepi*  32;  scales  104 
Tritylodon  43  ;  teeth  348 


Trochanter,  dog  412 ;  duck  326 

Trochilidae  42  ;5see  Humming-birds 

Trochlea,  crocodile  263;  dog  405  f.; 
duck  323 ;  turtle  232 

Trogon,  42 ;  foot  342 

Trogonidae  42 

Tropidouotus  38;  jaws  280;  skull 
279 

Trunk  vertebrae,  cod  84;  see  tho- 
racic and  lumbar  vertebrae 

Trygon  32;  calcification  of  verte- 
brae 114 ;  caudal  spine  106 

Trygonidae  32 

Tuberosities  of  humerus,  dog  405 ; 
of  ischium,  dog  411 

Tunicata  30,  51 

Tupaia,  skull  480;  thoraco-lumbar 
vertebrae  450 

Turbinals,  dog  395 

Tursiops  45 ;  skull  462 

Turtle  37 ;  anterior  limb  232,  234 ; 
cranium  222  f.,  226;  hyoid  231, 
285;  mandible  230;  pectoral 
girdle  231;  pelvic  girdle  235; 
pes  236;  plastron  217,  218;  pos- 
terior limb  234,  235;  sense  cap- 
sules 227;  skull  222;  vertebral 
column  219 ;  Leathery  — ,  see 
Dermochelys ;  Snapping  — ,  see 
Trionyx 

Tylopoda  45,  359 ;  fibula  519 ;  ma- 
nus 507  ;  odontoid  process  445  ; 
pelvis  514;  pes  523;  skull  468; 
teeth  428 ;  ulna  502 

Tympanic,  dog  392 ;  -  -  cavity, 
crocodile  250;  diagram  of  mam- 
malian 391;  dog  393;  duck 
315  f.;  turtle  228;  —  recess, 
duck  315 

Tympano-hyal,  dog  399 

Typhlopidae  38;  scales  270;  skull 
278 

Typhlops  38;  ischio-pubis  292; 
traces  of  posterior  limb  293 

Typotheriidae  46 

Typotherium  46,  358,  361;  clavicle 
495,  497;  femur  519;  pes  525; 
skull  472  ;  teeth  432 

Udenodon  36,  192 ;  beak  271 
Uintatheriidae  47;  skull  364 
Uintatherium  47;    dental  formula 
433;   leg  519;   limbs   and  limb 


558 


INDEX. 


girdles  516;  manus  510 ;  pelvis 

514;  skull  473 
Ulna  26;  crocodile  265;  dog  406; 

duck  323;  frog  164;  newt  147; 

turtle  233 

Ulnare  27 ;  see  Carpus 
Umbilicus,   inferior  and  superior, 

duck  303 
Unciuate  process  190;  crocodile  259; 

duck  320 

Unciform  27,  345,  504;  dog  408 
Ungulata  45 ;  auditory  ossicles  487 ; 

caudal    vertebrae  453;    cervical 

vertebrae  445 ;  general  characters 

357 ;  manus  506 ;  pectoral  girdle 

495 ;  pes  522 ;  ribs  491 ;  sacrum 

452;  skull  464  f.;  sternum  489; 

teeth  427  f. ;  thoraco-lumbar  ver- 
tebrae 448 
Ungulata  vera  45 ;  arm  bones  501 ; 

general  characters   358;    manus 

506;  pelvis  514;  thigh  and  shin 

519 
Upper  arm  26 ;  crocodile  263 ;  dog 

405;   duck  323;  frog  164;  newt 

147 ;  turtle  232 
Upupa  42  ;  see  Hoopoe 
Urochordata  30,  51 
Urodela    35]    general     characters 

134;  pelvis  187;  ribs  182;  skull 

174 

Urohyal,  cod  101 ;  duck  320 
Urostyle,  Anura  172;  cod  85;  frog 

153  ;  Teleostei  117 
Ursidae  48 ;  humerus  502 
Ursus  48 ;  dental  formula  439 ;  see 

Bears 

Vacuities,  anterior  palatine  — ,  cro- 
codile 252,  258 ;  —  in  reptilian 
skull  281 ;  posterior  palatine  — , 
crocodile  254,  257;  pre-orbital 
— ,  reptiles  283  f. 

Vampire  49;  teeth  441 

Vane,  of  feather  303 

Varanidae  38 

Varanus  38 ;  shoulder  girdle  2O2  ; 
skull  201 

Vasodentine  108,  272 

Vertebral  column  14;  Amphibia 
170;  birds  332;  cod  83;  croco- 
dile 239;  dog  378;  duck  307; 
Elasmobranchs  113;  frog  152; 


mammals  442 ;  newt  138 ;  turtle 

219 ;  —  ribs,  crocodile  259 ;  dog 

402 ;  duck  320 ;  —  shield,  turtle 

214 

Vertebrata,  general  characters  53 
Vexillum,  of  feather  303 
Vibrissae,  dog  374 
Viscacha  47 
Visceral   skeleton  21;   dogfish  77; 

Elasmobranchs  119  f. 
Viverra  48;  acetabular  bone  515 
Viverridae  48 
Vomer  21;  cod  98;  crocodile  252; 

dog  395;   duck  317;   frog   158; 

salmon  93 ;  turtle  229 
Vomero-palatine,  newt  143 
Vultur  41 
Vulture    41;   Black    — ,   shoulder 

girdle  and  sternum  337 

Waders  335 

Walrus  48,  367,  369;  canines  420; 
manus  511;  pes  526;  position 
of  limbs  29;  skull  480;  teeth 
440 

Warblers  42 

Wart  hog  45 ;  teeth  428 

Weasel  369 

Whale,  baleen  3,  418;  Ca'ing  - 
45,  see  Globicephalus ;  Hump- 
backed —  44,  357 ;  Right  —  44, 
357 ;  Sperm  —  44,  357,  see  Phy- 
seter;  True  or  Whalebone  —  356 

Whiting  33 

Wild  duck  41 ;  see  Duck 

Wing,  duck  322 ;  Gannet,  Ostrich, 
and  Penguin  339 

Wolf  48 

Wombat  43;  atlas  443;  pes  521; 
sacrum  451;  skull  456;  tail 
453 ;  teeth  423 

Woodpecker  42,  335;  foot  342; 
hyoid  336 

Wrasse  33 ;  teeth  111 

Xenacanthus  31 ;  pectoral  fins  130 

Xenopidae  36 

Xenopus  36;  branchial  arches  182; 

nails  168 ;  pelvis  188 ;  ribs  182 
Xiphiplastron,  turtle  217 
Xiphisterual  horn,  crocodile  260 
Xiphisternum,  dog  404 ;  frog  163 
Xiphoid  process,  duck  321 


INDEX.  559 

Zeuglodon    44,    353,    356 ;    dental  240  f . ;   dog  379  f. ;    duck  308  f. ; 

formula  426 ;  dermal  plates  420  frog    152  f. ;    newt    139 ;    turtle 

Zeuglodontidae  44  219  f. 

Zygantra,  denned  199  n. ;  reptiles  Zygosphene,  denned  199 n.;  reptiles 

276  276 
Zygapophyses,   cod  84;    crocodile 


CAMBRIDGE  :     PRINTED    BY   J.    AND    C.    F.    CLAY,    AT    THE    UNIVERSITY    PRESS. 


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All  of  importance  is  brought  forward  and  impartially  discussed.... Such  a 
book  has  long  been  a  desideratum.  Mr  Seward's  style  is  clear  and  concise, 
and  the  many  pitfalls  into  which  beginners  are  apt  to  stumble  are  clearly 
pointed  out. 


Cambridge  Biological  Series. 

Zoology.  An  Elementary  Text-Book.  By  A.  E. 
SHIPLEY,  M.A.,  F.R.S.,  and  E.  W.  MACBRIDE,  M.A.  (Cantab.), 
D.Sc.  (London),  Professor  of  Zoology  in  McGill  University,  Montreal. 
Demy  8vo.  With  nume'rous  Illustrations,  los.  6d.  Net. 

Pilot.     A  very  business-like  and  convenient  manual  of  modern  Zoology. 

School  World.  As  a  thoroughly  trustworthy  and  instructive  text-book 
for  serious  students,  the  work  can  be  strongly  recommended.  Its  value  is 
enhanced  by  the  large  number  of  excellent  illustrations,  many  of  which  are 
delightfully  fresh. 

Oxford  Magazine.  It  is  readable,  well  arranged,  well  printed,  copiously 
and  admirably  illustrated,  and  it  covers  the  whole  field  of  zoology. 

Nature.  There  pervades  the  pages  of  the  work  a  freshness  of  style  and 
unconventionality  which  render  them  pleasant  reading  and  attractive ; 
while,  in  the  frequent  allusion  to  the  commonest  occurrences  of  daily  life 
and  human  affairs,  the  interest  of  the  reader  is  assured. 

Pall  Mall  Gazette.  Precisely  the  sort  of  book  which,  if  it  came  into  a 
thoughtful  boy's  hands,  would  turn  him  from  a  smatterer  into  a  student — 
One  of  the  most  instructive  and  attractive  books  that  could  be  put  into  the 
hands  of  a  young  naturalist. 

Grasses  :  a  Handbook  for  use  in  the  Field  and  Laboratory. 
By  H.  MARSHALL  WARD,  Sc.D.,  F.R.S.,  Fellow  of  Sidney  Sussex 
College,  Professor  of  Botany  in  the  University  of  Cambridge.  With 
8 1  figures.  Crown  8vo.  6>. 

Pilot.     Brimful  of  matter. 

Field.  The  work  is  essentially  suited  to  the  requirements  of  those 
desirous  of  studying  the  grasses  commonly  grown  in  this  country,  and 
it  can  fairly  be  said  that  it  furnishes  an  amount  of  information  seldom 
obtained  in  more  pretentious  volumes. 

Athen&um.  Botanists  and  Agriculturists  alike  have  reason  to  thank 
Prof.  Ward  for  this  very  serviceable  addition  to  the  literature  of  grasses. 

Trees  :  A  Handbook  of  Forest  Botany  for  the  Woodlands 
and  the  Laboratory.  By  H.  MARSHALL  WARD,  Sc.D.,  F. R.S., 
Fellow  of  Sidney  Sussex  College,  Honorary  Fellow  of  Christ's  College 
and  Professor  of  Botany  in  the  University  of  Cambridge.  In  six 
volumes.  i.  Buds  and  Twigs,  2.  Leaves,  3.  Inflorescences  and 
Flowers,  4.  Fruits  and  Seeds,  5.  Seedlings,  6.  General  Characters. 
Vol.  I.  Buds  and  Twigs.  Crown  8vo.  Illustrated.  4,5-.  6d.  net. 

A  Treatise  on  the   British   Freshwater   Algse.     By 

G..S.  WEST,  M.A.,  A.R.C.S.,  F.L.S.,  Professor  of  Natural  History 
at  the  Royal  Agricultural  College,  Cirencester.  Demy  8vo.  los.  6d.  net. 

A  Manual  and  Dictionary  of  the  Flowering  Plants 

and  Ferns.  By  J.  C.  WILLIS,  M.A.,  Director  of  the  Royal  Botanic 
Gardens,  Ceylon.  Second  Edition.  Complete  in  one  volume.  Crown 
8vo.  los.  6d. 

P.  T.  O. 


Cambridge  Biological  Series. 
Elementary  Palaeontology— Invertebrate.     By  HENRY 

WOODS,  M.A.,  F.G.S.,  University  Lecturer  in  Palseozoology.  Crown 
8vo.  Third  Edition.  Revised  and  enlarged,  with  112  Illustrations. 
6s. 

Outlines  of  Vertebrate   Palaeontology  for  students 

of  Zoology.  By  ARTHUR  SMITH  WOODWARD,  M.A.,  F.R.S., 
Keeper  of  the  Department  of  Geology  in  the  British  Museum.  Demy 
8vo.  With  numerous  Illustrations,  i^s. 

Athenceum.  The  author  is  to  be  congratulated  on  having  produced  a 
work  of  exceptional  value,  dealing  with  a  difficult  subject  in  a  thoroughly 
sound  manner. 


In  preparation. 

Morphology  and  Anthropology.  By  W.  L.  H. 
DUCKWORTH,  M.A.,  Fellow  and  Lecturer  of  Jesus  College,  University 
Lecturer  in  Physical  Anthropology. 

The   Origin    and    Influence    of   the    Thorough-bred 

Horse.  By  W.  RIDGKWAY,  M.A..  Disney  Professor  of  Archaeology 
and  Fellow  of  Gonville  and  Caius  College.  With  numerous  Illustra- 
tions. Demy  8vo. 

The  Morphology  of  Plants.     By  J.  C.  WILLIS,  M.A. 


HonDon:   C.   J.    CLAY   AND   SONS, 

CAMBRIDGE   UNIVERSITY    PRESS   WAREHOUSE, 
AVE   MARIA   LANE, 

AND 

H.  K.  LEWIS,   136,  GOWER   STREET,   W.C. 
:    50,   WELLINGTON   STREET 


UNIVERSITY  OF  CALIFORNIA  MEDICAL  SCHOOL  LIBRARY 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


NOV  21 
APR  4  -  J923 


/J84Q 

944 

MAR  4-  1944 
APR  2  4 


.w-11,'18 


Arnolds.    3. 
R46  The  vertebrate 


keleton. 


9  1    109^'OV  1  1  1924 


APR  4  -  1929 


./APR  18  192bAPR  20  1929 


-fllpR   30  194S 


University  of  CaUfornia  Medical  School  Library 


